Document implicit naming convention

[aaronlevin]

We should update the contributing guidelines to specify implicit naming convention. I believe the convention is to prefix the name of the implicit with a camel-cased version of the package namespace. See quote from @peterneyens on a ticket I was working on (adding Traverse instances in the cats.free package):

It is not really documented outside issue #1061 itself (it should probably be added to these guidelines): the implicit values in Cats are prefixed with the package.

So these implicits would be catsFreeFoldableForFree and catsFreeTraverseForFree.

[tbje]

Hey @aaronlevin, did #1920 fix this issue?

[kailuowang]

fixed by #1920 thanks again @tbje