Move the list of third-part plugins into the user manual

[szabgab]

Problem

When searching for epub on https://rust-lang.github.io/mdBook/ there is no hit. When searching for pdf there is only one hit, but it does not show how.

Proposed Solution

IMHO it would be better to move the list of third-party-plugins from https://github.com/rust-lang/mdBook/wiki/Third-party-plugins to the user manual. That way it will be easier to find them.

Notes

No response

[szabgab]

@ehuss, I'd be happy to send the PR, if you think this is a good idea.

[ehuss]

We used to have it in the guide, but it was moved to the wiki due to the trouble of maintaining the list, and the issues with delayed deployment. After moving, the list ended up getting far more updates and was much larger. I think for now I would prefer to keep it that way. I understand there's a limitation with searching, but I don't have a really good answer for that.

[szabgab]

I see.
Maybe we could automatically copy the content into the user-guide upon the release?
It could say that this page is a copy from the wiki and it could include a link for people interested updating it.