A couple of small typos in the manual

Hi Prot!

Just received the update, and am already enjoying it. Thank you! Great release, as usual!

And since it'd been some time since I'd gone through the docs, I took a look at the manual, and noticed a couple of typos in it, which I report quickly.

In section "4.12 Option for language checkers", the first sentence contains leaves the original foreground in tact, where it should be "intact".

Section "4.20 Option for the headings’ overall style" is missing existing option rainbow-no-bold.