add script to update Xcode compatibility

$ ./update_compat.sh

README.markdown

@@ -27,6 +27,10 @@ XcodeColors is a simple plugin for Xcode 3, 4, 5 & 6
 
 Did you **upgrade Xcode** and now XcodeColors is **"broken"**? Get the fix here: **[XcodeUpdates](https://github.com/robbiehanson/XcodeColors/wiki/XcodeUpdates)**.
 
+```
+$ ./update_compat.sh
+```
+
 ### XcodeColors installation instructions for Xcode 3:
 
 Wow, you're still running Xcode 3?  

update_compat.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+# show Xcode version and UUID
+xcodebuild -version
+uuid=$(defaults read /Applications/Xcode.app/Contents/Info DVTPlugInCompatibilityUUID)
+echo "UUID $uuid"
+echo ""
+
+# check UUID
+plist=$(pwd)/XcodeColors/Info
+if [ -n "$(defaults read '$plist' | grep $uuid)" ] ; then
+    echo "UUID is already added to Info.plist"
+    exit
+fi
+
+# add UUID to .plist
+echo "Add UUID to '$plist'"
+defaults write '$plist' DVTPlugInCompatibilityUUIDs -array-add $uuid
+
+# show the result
+defaults read '$plist'