Hi! There are detailed guides for all of the official integrations – you can find them in the help docs. Each integration’s article has a step-by-step guide. Those integrations are made by Beeminder’s team, and tested and documented before release.
I don’t currently track or document unofficial integrations in the help docs, because we have no control over them and we don’t want to give people the wrong impression. There are some really great third-party integrations, and I know about a fair number, but it’s very hard to write and maintain documentation about third-party stuff we don’t control. It’s so much to track!
Which is not to say I won’t give thought to some kind of help doc that lists stuff we know of, at the very least. 
That might be possible.
As far as an official Anki integration goes, they don’t have an API and it’s my understanding they don’t plan to have one either, which sort of rules them out as an official integration. That’s why the workarounds are all a bit clunky in some way (when I used it, I’d always have to remember to sync my phone app to Anki Web, and then sync Anki Web to the desktop app, for example). But we do keep an eye out for promising opportunities, because we know an Anki integration would be amazing for a lot of users.
This thread in the forum is the one about the most commonly used Anki add-on (at least in my experience). If you have any questions about that particular add-on, it’s also a good place to ask.