doc: suggest nodejs/help for general support

This commit adds a reference to `nodejs/help` in the github template.

PR-URL: https://github.com/nodejs/node/pull/9128


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>