Make sublime-project rule off by default

Global/SublimeText.gitignore

@@ -1,4 +1,6 @@
-# SublimeText project files
+# workspace files are user-specific
 *.sublime-workspace
 
-# *.sublime-project should be checked into the repository as a general rule
+# project files should be checked into the repository, unless a significant
+# proportion of contributors will probably not be using SublimeText
+# *.sublime-project