The following strategy worked when I added something to pgfpages
1. create sourceforge account if you don't already have one
2. fork repository from https://sourceforge.net/p/pgf/git/ci/master/tree/ (there is a button "Fork" in the left had sidebar) and follow instructions that appear
3. To get it on your computer: `git clone ssh://
[email protected]/u/marmot/pgf pgf` (replace marmot with your user name)
4. Adding the original repository to get all the stuff other people are doing: `git remote add upstream https://git.code.sf.net/p/pgf.git`