For contributers, please "Sync fork" instead of "git merge" readme note (#888)

README.md

@@ -254,6 +254,9 @@ Then use the `gen_ui_files` scripts to autogenerate the python UI.
 
 An example PR adding a new checkbox is here: https://github.com/ciromattia/kcc/pull/785
 
+Do not use `git merge` to merge master from upstream, 
+use the "Sync fork" button on your fork on GitHub in your branch 
+to avoid weird looking merges in pull requests.
 
 ### Windows install from source