Update .gitignore and some comments.

.gitignore

@@ -16,6 +16,7 @@
 *.d
 *.sdf
 xcuserdata
+*.xccheckout
 contents.xcworkspacedata
 .DS_Store
 .svn

modules/juce_audio_plugin_client/AU/juce_AU_Wrapper.mm

@@ -56,6 +56,13 @@
  #define Component CarbonDummyCompName
 #endif
 
+/*
+    Got an include error here?
+
+    You probably need to install Apple's AU classes - see the
+    juce website for more info on how to get them:
+    http://www.juce.com/forum/topic/aus-xcode
+*/
 #include "AUMIDIEffectBase.h"
 #include "MusicDeviceBase.h"
 #undef Point