There is an existing Open Source Project, say A, on GitHub which I have cloned. I have some requirements which will need modifying some of the features of this Open Source Project. So, I was thinking of creating a new Git Repository with the latest code of A and commit all my changes to this new repository, say B.
However, if there are any new changes in A, I would like to merge them with my project B. (I don't want to commit my changes to A).
I have never used GitHub (only used SVN). What is the best way of doing this?