approve

$ git pr approve -h
usage: git-pr [options] [<ID>]
        -u, --username NAME  Username on host
        -r, --remote NAME    Name of remote, defaults to 'origin'
        -m, --message TEXT   Message to author as part of approval (e.g. "Looks good!")
            --verbose        Turn on verbose output
            --debug          Turn on debugging output
            --version        Print the version of this tool
        -h, --help           Show this help text

$ git pr approve 756

$ git pr approve -m LGTM 756