GitIgnore: Add qbs.user files

Change-Id: I9aae36188ed11d0a7211dbe3e079d4c0fc2ab272
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

.gitignore

@@ -35,6 +35,7 @@ Thumbs.db
 
 # qtcreator generated files
 *.pro.user*
+*.qbs.user*
 *.qmlproject.user*
 *.pluginspec
 *.json