Update .gitignore

.gitignore

@@ -1,3 +1,21 @@
+# -----------------------------------------------------------------
+# .gitignore
+#
+# This file specifies intentionally untracked files to ignore
+# http://git-scm.com/docs/gitignore
+#
+# NOTES:
+# The purpose of gitignore files is to ensure that certain files not
+# tracked by Git remain untracked.
+#
+# To ignore uncommitted changes in a file that is already tracked,
+# use `git update-index --assume-unchanged`.
+#
+# To stop tracking a file that is currently tracked,
+# use `git rm --cached`
+#
+# -----------------------------------------------------------------
+
 # Compiled Lua sources
 luac.out