Merge #14207: doc: -help-debug implies -help

Summary:
d0b1cee1fe95eba7b968bed2c33ab681d169c91f doc: -help-debug implies -help (Wladimir J. van der Laan)

Pull request description:

I don't understand why `-help-debug` would be useful without requesting the help, and I've made this particular mistake one time too many.

Tree-SHA512: 370eab368d672fc09e66fcc440db3cb7e4c70c2988aab506cdc3f3e234c27c8f0fc7512c9cf86606ac43f5c6023b3618b7b0302b4b6e289b388559ba8010f27a

Backport of Core PR14207

Test Plan:

ninja
./bitcoind --help-debug

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5486