Add a documentation page for Nested

[cb372]

If anyone has more motivating examples, I'm happy to add them.

[LukaJCB]

This was long overdue thanks a bunch for working on it! 👏

One thing we should do in the future is to replace the instances of Future we have in parts of our documentation with IO, but for now it's alright :)

[cb372]

Yeah actually the example we discussed on Twitter originally used IO but I "downgraded" it to Future :)

I guess porting the examples to IO would mean adding a library dependency on cats-effect for the docs module. That feels a little weird. Or move the docs module into its own repo? That has its downsides as well: it means you can't add a new feature and write the docs for it at the same time.

[codecov-io]

Codecov Report

Merging #2369 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2369   +/-   ##
=======================================
  Coverage   95.01%   95.01%           
=======================================
  Files         349      349           
  Lines        5998     5998           
  Branches      221      222    +1     
=======================================
  Hits         5699     5699           
  Misses        299      299

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[LukaJCB]

Yeah we've had the discussion before about Free and what we'd interpret into. I think we could definitely take a dependcy just for the docs module once cats-effect is stable :)

[kailuowang]

@LukaJCB having cats-effect as a dependency in docs might make things hairy when we start to have breaking changes (say going 3.0), but I guess in that case we need to coordinate with Cats-effect anyway. So 👍

[kailuowang]

thanks so much!