However, I am not really sure what I am doing with GitHub. I think (or at least hope) that what I have done is merge the changes that have occurred in this main repository into my own fork, then made changes in my own fork, then issued a pull request such that my changes to my own fork could be considered for the main repository. But I'm not at all sure I did the first step correctly — I don't know how to do that on the commandline, so I used GitHub's interface, which I am not used to.
However, I am not really sure what I am doing with GitHub. I think (or at least hope) that what I have done is merge the changes that have occurred in this main repository into my own fork, then made changes in my own fork, then issued a pull request such that my changes to my own fork could be considered for the main repository. But I'm not at all sure I did the first step correctly — I don't know how to do that on the commandline, so I used GitHub's interface, which I am not used to.