Update docs for new config available files.

[AdeAttwood]

Do we need to update the docs for this?
Just saw this: #83 (comment)

Originally posted by @escapedcat in #2698 (comment)

If someone has time, please create a PR to update the docs:

• https://github.com/conventional-changelog/commitlint/blob/master/README.md#config
• https://github.com/conventional-changelog/commitlint/blob/master/docs/guides-local-setup.md#install-commitlint

Thanks!

(#83 (comment))

[escapedcat]

@AdeAttwood sorry, after updating your issue here I just remembered that this was done here already I think:
https://github.com/conventional-changelog/commitlint/pull/2728/files

[ruigazio]

With the new config file formats, how to state the plugins section in JSON or YAML?

#699

In the example of this issue above, and when "transcoding" the file into JSON, the value of dolar-sign can be a string, not a function.