This should be obvious to advanced users, but we got a report from a
novice user that they initially didn't realize that this step was
needed. Of course, we can't guarantee that they'll read this sentence,
but it can't hurt to add.
Another alternative would be to provide a copy/pasteable push command,
but reconstructing the exact push command the user used the first time
is nontrivial and possibly infeasible, due to remote names, local
refnames, `git push` flags, etc. This natural language sentence is
comparatively trivial to add.
Change-Id: I81994084da61fec4fef329b1715dd5488ebe2a21
da7f2478cb