It's useful to know when you've modified a branch that exists on a
remote. A typical case is when you have pushed a branch to a remote
and then rewritten it. This commit adds an indication in the
`branches` template keyword. A branch that needs to be pushed to a
remote now has a `*` at the end (similar to how conflicted branches
have a `?` at the end). Note that the indication only considers
remotes where the branch currently exists, so there won't be an
indication that the branch has not been pushed to a remote.
Closes#254
I wanted to have all the documentation available on the command line,
but that makes it harder to maintain and link to. Let's move it to
markdown instead. We may later be able to add some way of presenting
the markdown in the terminal (or maybe by first converting it to
reStructuredText).
