update docblock for add_command() to properly reflect the return value
update docblock for add_command() to properly reflect the return value

trepmal/wp-cli,aaemnnosttv/wp-cli,aaemnnosttv/wp-cli,rodrigoprimo/wp-cli,rodrigoprimo/wp-cli,trepmal/wp-cli,trepmal/wp-cli,aaemnnosttv/wp-cli,rodrigoprimo/wp-cli