Thanks for all the great feedback so far, guys. I've also added some examples for tracking entire repositories by branch, and an example of how to add those dir

Thanks for all the great feedback so far, guys. I've also added some examples for tracking entire repositories by branch, and an example of how to add those directories to your `.gitignore` in case you don't want all their files pull in, but want to `git fetch-fill pull` after cloning.