Add reference directory to gitignore

- Prevents reference materials from being tracked
- Removes reference/android-original from git tracking
- Keeps reference directory local for development use

.gitignore

@@ -48,6 +48,9 @@ nohup.out
 
 # OS
 .DS_Store
+
+# Reference directories
+reference/
 .DS_Store?
 ._*
 .Spotlight-V100