Updated README:

* Added instructions on installing prerequisites in (Ubuntu) Linux.
 * Added instructions on how to use vagrant for development.
 * Minor copy-editing.

pch: rebased pullreq 183

README.md

@@ -2,49 +2,121 @@
 
 ## Getting the source
 
-You can either download the source using the "ZIP" button at the top of the
-github page, or you can make a clone using git:
+You can either download the source using the "ZIP" button at the top
+of the github page, or you can make a clone using git:
 
 ```
 git clone git://github.com/diydrones/ardupilot.git
 ```
 
-## Building using Arduino IDE
+## Prerequisites
 
-ArduPilot is no longer compatible with the standard Arduino distribution.
-You need to use a patched Arduino IDE to build ArduPilot.
+### Ubuntu Linux
 
-1. The patched ArduPilot Arduino IDE is available for Mac and Windows from
-   the [downloads page][1]. On Linux, you should use the makefile build.
+The following packages are required to build ardupilot for the
+APM1/APM2 (Arduino) platform in Ubuntu: `gawk make git arduino-core
+g++`
 
-2. Unpack and launch the ArduPilot Arduino IDE. In the preferences menu, set
-   your sketchbook location to your downloaded or cloned `ardupilot` directory.
+To build ardupilot for the PX4 platform, you'll first need to install
+the PX4 toolchain and download the PX4 source code.  See the [PX4
+toolchain installation
+page](https://pixhawk.ethz.ch/px4/dev/toolchain_installation_lin).
 
-3. In the ArduPilot Arduino IDE, select your ArduPilot type (APM1 or APM2) from
-   the ArduPilot menu (in the top menubar).
+The easiest way to install all these prerequisites is to run the
+`ardupilot/Tools/scripts/install-prereqs-ubuntu.sh` script, which will
+install all the required packages and download all the required
+software.
 
-4. Restart the ArduPilot Arduino IDE. You should now be able to build ArduPlane
-   or ArduCopter from source.
 
-5. Remember that, after changing ArduPilot type (APM1 or APM2) in the IDE,
-   you'll need to close and restart the IDE before continuing.
+## Building using the Arduino IDE
 
-[1]: http://code.google.com/p/ardupilot-mega/downloads/list
+ArduPilot is no longer compatible with the standard Arduino
+distribution.  You need to use a patched Arduino IDE to build
+ArduPilot.
+
+Do not try to use the Arduino IDE to build in Linux--you should follow
+the instructions in the "Building using make" section.
+
+1. The patched ArduPilot Arduino IDE is available for Mac and Windows
+   from the [downloads
+   page](http://code.google.com/p/ardupilot-mega/downloads/list).
+
+2. Unpack and launch the ArduPilot Arduino IDE. In the preferences
+   menu, set your sketchbook location to your downloaded or cloned
+   `ardupilot` directory.
+
+3. In the ArduPilot Arduino IDE, select your ArduPilot type (APM1 or
+   APM2) from the ArduPilot menu (in the top menubar).
+
+4. Restart the ArduPilot Arduino IDE. You should now be able to build
+   ArduPlane or ArduCopter from source.
+
+5. Remember that, after changing ArduPilot type (APM1 or APM2) in the
+   IDE, you'll need to close and restart the IDE before continuing.
 
 
 ## Building using make
 
- 1. Before you build the project for the first time, you'll need to run
-    `make configure` from a  sketch directory. This will create a `config.mk`
-    file at the top level of the repository. You can set some defaults in
-    `config.mk`
+ 1. Before you build the project for the first time, you'll need to
+    run `make configure` from a sketch directory, for example
+    `ardupilot/ArduCopter` . This will create an `ardupilot/config.mk`
+    file. You can set some defaults in `ardupilot/config.mk`.
 
- 2. In the sketch directory, type `make` to build for APM2. Alternatively,
-    `make apm1` will build for the APM1.
+ 2. In the sketch directory, type `make` to build for
+    APM2. Alternatively, `make apm1` will build for the APM1 and `make
+    px4` will build for the PX4.
 
  3. Type `make upload` to upload. You may need to set the correct default
     serial port in your `config.mk`.
 
+
+## Development using VirtualBox
+
+ardupilot has a standardized Linux virtual machine (VM) setup script
+that uses the free VirtualBox virtualization software.  You can use it
+to create a standard, reproducible development environment in just a
+few minutes in Linux, OS X, or Windows.
+
+ 1. [Download VirtualBox](https://www.virtualbox.org/wiki/Downloads)
+ for your Mac, Windows or Linux machine.
+
+ 2. [Install vagrant](http://docs.vagrantup.com/v2/installation/).
+
+ 4. In the `ardupilot` directory, run `vagrant up` from the command
+ line.  This will create a new Ubuntu Linux VM.
+
+ 5. Run `vagrant ssh -c
+ "ardupilot/Tools/scripts/install-prereqs-ubuntu.sh -y"`.  This will
+ install all the prerequisites for doing ardupilot development.
+
+You can now run `vagrant ssh` to log in to the development
+environment.  The `~/ardupilot` directory in the VM is actually the
+`ardupilot` directory in your host operating system--changes in either
+directory show up in the other.
+
+Once you've followed the instructions above, here's how you would
+build ArduCopter for PX4 in the development environment:
+
+```
+$ vagrant ssh
+# cd ardupilot/Arducopter
+# make configure
+```
+
+Now edit `ardupilot/config.mk` so it has the following line:
+
+```
+PX4_ROOT = ~/PX4-Firmware
+```
+
+Back at the terminal:
+
+```
+# cd ~/PX4-Firmware
+# make configure_px4fmu
+# make px4
+```
+
 # User Technical Support
 
 ArduPilot users should use the DIYDrones.com forums for technical support.
@@ -53,9 +125,8 @@ ArduPilot users should use the DIYDrones.com forums for technical support.
 
 The ArduPilot project is open source and maintained by a team of volunteers.
 
-To contribute, you can send a pull request on Github. You can also join the
-[development discussion on Google Groups][2]. Note that the Google Groups
-mailing lists are NOT for user tech support, and are moderated for new users to
-prevent off-topic discussion.
-
-[2]: https://groups.google.com/forum/?fromgroups#!forum/drones-discuss
+To contribute, you can send a pull request on Github. You can also
+join the [development discussion on Google
+Groups](https://groups.google.com/forum/?fromgroups#!forum/drones-discuss). Note
+that the Google Groups mailing lists are NOT for user tech support,
+and are moderated for new users to prevent off-topic discussion.