completion: add docs on how to add subcommand completions

Signed-off-by: Roland Hieber <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: rohieb

contrib/completion/git-completion.bash

@@ -31,6 +31,13 @@
 # Note that "git" is optional --- '!f() { : commit; ...}; f' would complete
 # just like the 'git commit' command.
 #
+# To add completion for git subcommands that are implemented in external
+# scripts, define a function of the form '_git_${subcommand}' while replacing
+# all dashes with underscores, and the main git completion will make use of it.
+# For example, to add completion for 'git do-stuff' (which could e.g. live
+# in /usr/bin/git-do-stuff), name the completion function '_git_do_stuff'.
+# See _git_show, _git_bisect etc. below for more examples.
+#
 # If you have a shell command that is not part of git (and is not called as a
 # git subcommand), but you would still like git-style completion for it, use
 # __git_complete. For example, to use the same completion as for 'git log' also