Add branch to config

[surmann]

Hallo and thank you for that easy tutorial in so many languages.

I got an issue when start working on a new branch. I was not able to push it in RStudio (a normal git push worked), because the branch has no entry in the config file. The command git branch --set-upstream myBranch origin/myBranch for branch myBranch solved this problem. Perhaps you can add this as the last command in the branching section.

Kind regards Dirk