31.0: add RPC docs

[Sjors]

See #1187 for the previous doc update.

[polespinasa]

ACK cd948c6

I did ran the script myself and got the same result

$ git log --oneline -n2
717a951 (HEAD -> master) generated by me
667555a (upstream/master, origin/master, origin/HEAD) Merge bitcoin-core/bitcoincore.org#1244: doc: Add my key to contacts
sliv3r@sliv3r-tuxedo:~/Documentos/Projectes/BitcoinCore/bitcoincore.org/contrib/doc-gen$ git checkout pr-1245 
Switched to branch 'pr-1245'
sliv3r@sliv3r-tuxedo:~/Documentos/Projectes/BitcoinCore/bitcoincore.org/contrib/doc-gen$ git cherry-pick 717a951
On branch pr-1245
You are currently cherry-picking commit 717a951.
  (all conflicts fixed: run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

nothing to commit, working tree clean
The previous cherry-pick is now empty, possibly due to conflict resolution.
If you wish to commit it anyway, use:

    git commit --allow-empty

Otherwise, please use 'git cherry-pick --skip'

[fanquake]

cc @stickies-v

[stickies-v]

ACK cd948c6

I'm getting the same diff, and reviewing the diff with v30.0 I couldn't see any obvious bugs.

[Sjors]

Looks OK on production too: https://bitcoincore.org/en/doc/31.0.0/