$ git mv old_filename new_filename
# Short answer:
git mv filename new_filename
or
git mv /path/to/file_location /path/to/new/file_location
# Note, if you manually move a file or rename it (w/o git mv) git may
# treat the moved/renamed file as a new file
# Note, it's fairly popular to use the alias gm for git mv
$ git clone git@github.com:username/reponame.git
$ cd reponame
$ git mv README README.md
$ git commit -m "renamed"
$ git push origin master
git mv old_file new_file
git mv dir1/somefile.js dir2
git mv file_from file_to