Import git repo into another repo while keeping the history of both.

gistfile1.txt

//From http://stackoverflow.com/a/8396318/657977

Switch [NAME] for whatever name you want to call it
Switch [PATH or URL] for the path or url to the repo you want to include.

git remote add [NAME]_remote [PATH or URL]
git fetch [NAME]_remote
git merge -s ours --no-commit [NAME]_remote/master
git read-tree --prefix=[NAME]/ -u [NAME]_remote/master
git commit -m "Imported [NAME] as a subtree."