Added link to source

Umbraco.gitignore

@@ -1,3 +1,7 @@
+## Ignore Umbraco files/folders generated for each instance
+##
+## Get latest from https://github.com/github/gitignore/blob/master/Umbraco.gitignore
+
 # Note: VisualStudio gitignore rules may also be relevant
 
 # Umbraco