Issue on page /opensource/community_development.html#making-a-change

[celprov]

To keep up with changes, add the “upstream” repository as a remote to your locally cloned repository.
Keep your fork up to date with the upstream repository.

For me that is not familiar with Github, I don't understand the concept of upstream repository. Can you add a sentence explaining more precisely the concept ?

[josephmje]

Done in #34