Add comment to prevent *.sublime-project being ignored.

Based on advice in the documentation at
http://www.sublimetext.com/docs/2/projects.html

Global/SublimeText.gitignore

@@ -1,2 +1,4 @@
 # SublimeText project files
 *.sublime-workspace
+
+# *.sublime-project should be checked into the repository as a general rule