Doc: new Git commands

Actions on Commits, Fixup Last Commit, Interactive Rebase,
Rename branch, Push to remote repository, and Push to Gerrit

Change-Id: I434f836944d9fa86fad73f0256b330aad9532ed0
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Petar Perisin <petar.perisin@gmail.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>