waf: add documentation for build shortcuts

wscript

@@ -191,9 +191,21 @@ class CheckContext(BuildContext):
     '''executes tests after build'''
     cmd = 'check'
 
-ardupilotwaf.build_shortcut('copter', targets='bin/arducopter')
-ardupilotwaf.build_shortcut('plane', targets='bin/arduplane')
-ardupilotwaf.build_shortcut('rover', targets='bin/ardurover')
+ardupilotwaf.build_shortcut('copter',
+    targets='bin/arducopter',
+    doc='builds arducopter',
+)
+ardupilotwaf.build_shortcut('plane',
+    targets='bin/arduplane',
+    doc='builds arduplane',
+)
+ardupilotwaf.build_shortcut('rover',
+    targets='bin/ardurover',
+    doc='builds ardurover',
+)
 
 for program_group in ('all', 'bin', 'tools', 'examples', 'tests', 'benchmarks'):
-    ardupilotwaf.build_shortcut(program_group, program_group_list=program_group)
+    ardupilotwaf.build_shortcut(program_group,
+        program_group_list=program_group,
+        doc='builds all programs of %s group' % program_group,
+    )