Merge branch 'po/help-guides'

"git help" learned "-g" option to show the list of guides just like list of commands are given with "-a". * po/help-guides: doc: include --guide option description for "git help" help: mention -a and -g option, and 'git help <concept>' usage. builtin/help.c: add list_common_guides_help() function builtin/help.c: add --guide option builtin/help.c: split "-a" processing into two