Copter: update release notes to add slow take-off

ArduCopter/ReleaseNotes.txt

@@ -15,10 +15,12 @@ Improvements over 3.0.1
     a) motors always spin when armed (speed can be controlled with MOT_SPIN_ARMED, set to 0 to disable)
     b) vehicle's maximum lean angle can be reduced (or increased) with the ANGLE_MAX parameter
     c) arming check that GPS hdop is > 2.0 (disable by setting GPS_HDOP parameter to 900)
+    d) slow take-off in AUTO, LOITER, ALTHOLD to reduce chance of motor/esc burn-out on large copters
 7) Bug fixes:
     a) Optical flow sensor initialisation fix
     b) altitude control fix for Loiter_turns mission command (i.e. mission version of CIRCLE mode)
     c) DO_SET_ROI fix (do not use "ROI")
+8) Distribute Loiter & Navigation calcs over 4 cycles to reduce impact on a single 100hz loop
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 ArduCopter 3.0.1-rc2 / 3.0.1 11-Jul-2013
 Improvements over 3.0.1-rc1