Added documentation for doctest formatting tools

[samuelikohn]

Description

Addresses issue #3083. Adds a documentation page under integration for tools that can apply Black formatting to doctests. This is meant to inform users of 3rd party tools that cover functionality not covered by Black. New doc page includes a brief description of blackdoc and blacken-docs. The integrations index page was also updated to list this new page.

Checklist - did you ...

• Implement any code style changes under the --preview style, following the
  stability policy?

• Add an entry in CHANGES.md if necessary?

• Add / update tests if necessary?

• Add new / update outdated documentation?

• Updated CHANGES.md

• Confirmed documentation pages build as expected

[cobaltt7]

I'm a bit hesitant about advertising small third-party tools that integrate directly with Black. One issue that comes to mind (beyond the obvious security concerns) is #4757, where a similar small project started crashing after we changed our public API, which is not stable or covered under semver (see #779).

Do the maintainers of these packages know that we're considering linking to them on our docs?

[samuelikohn]

I'm a bit hesitant about advertising small third-party tools that integrate directly with Black. One issue that comes to mind (beyond the obvious security concerns) is #4757, where a similar small project started crashing after we changed our public API, which is not stable or covered under semver (see #779).

Do the maintainers of these packages know that we're considering linking to them on our docs?

That's a fair point. My interpretation of the discussion around #3083 was that this would be a nice-to-have. The wording can certainly be changed, but based on the issues you brought up it may be best to scrap the issue altogether. But afaik the maintainers haven't been contacted.