This still referred to a config file format prior to 49d11acde0. Reword
sections accordingly and try to explain the actual configuration file format.
xmltoman is quite limited in its supported tags, so we need to use wrong tags
to get some sensible formatting, notably <opt> to get a bold word.
This tool detects and fixes common English spelling mistakes, with
generally very few mistakes.
Here is the command I used to generate this commit. There were a few
changes that had to be done manually, and of course adding the ignore
file:
```shell
codespell -I .codespell-ignore -x .codespell-ignore -w
```
I didn’t add it to the CI, but this would be a good place for it.