title: How do I "commit" changes in a git submodule?
body: <p>I have, in my naivety, set up a git submodule and treated it like a Subversion external - i.e. it's now full of changes that I've just realized haven't been committed or pushed anywhere.</p>
  
  <p>Is there some easy way to commit/push the submodule changes back to the upstream repo? And what's the recommended technique in Git for doing simultaneous development on separate (but linked) repositories in this way?</p>