Add --help for all commands.

[nodejs]

Add --help for all commands.

[gibfahn]

I think it's worth doing, and the standard that I've seen in other projects is to add a help subcommand, so you can do node-gyp help configure to get the help for configure.

[japj]

did you have any ideas on how to implement this? I just got a person asking for "how do I convince node-gyp to stop trying to use the damn downloaded headers", i.e. use --nodedir ;)

[TooTallNate]

@japj Probably something simple like an exports.help String on each command's exports. Feel like a pull request? ;)

[Trott]

Is this still considered a desirable addition? If so, maybe we can add a "help wanted" or "good first contribution" label? If not, then I guess we should close the issue. @nodejs/node-gyp

[owl-from-hogvarts]

Any progress here?