Sync docs for belt_Set.mli

[whitchapman]

Please let me know if I am on the right track. I am basically replacing the comments with the raw comments from rescript-lang.

[whitchapman]

I was attempting to stick with doing all of the Set modules but ran into a couple of issues:

• there is not a corresponding mdx file for belt_Set.cppo.mli [and I do not know what cppo indicates]
• when looking at belt_MutableSet.mli, noticed inconsistency between the usage of ('k,'id) and ('value, 'id) -- I figure this should be consistent throughout the modules but that would require changing code. Please advise.

[ryyppy]

Sorry for my late review.

Great work so far! The most important thing is to remove the leading res sig for each doc string, since it would just duplicate the actual function signature.

[whitchapman]

...remove the leading res sig for each doc string, since it would just duplicate the actual function signature.

I removed all duplicate signatures from all 6 files. Seems obvious in hindsight 😄 @ryyppy

[ryyppy]

looking good now. thanks!