git -again

 error:

git pull origin

You are not currently on a branch.
Please specify which branch you want to merge with.
See git-pull(1) for details.
   git pull <remote> <branch>

so...

git checkout master
Switched to branch 'master'
Your branch is up-to-date with 'origin/master'.

Now you can:

git checkout master
Switched to branch 'master'
Your branch is up-to-date with 'origin/master'.