Move yieldsAsync* documentation to the first yieldsAsync*

[malev]

Purpose (TL;DR) - mandatory

Move the description for yieldsAsync* methods to the first yieldsAsync* because it makes more sense to be there.

Background (Problem in detail) - optional

If you visit http://sinonjs.org/releases/v4.1.2/stubs/, at first glance it looks like the yieldsAsync* methods lack on documentation.
The generic explanation for all the yieldsAsync* is under yieldsToOnAsync which is the last method on the list
Makes more sense to have the generic documentation under the first yieldsAsync* of the list.

How to verify - mandatory

1. Check out this branch
2. npm install

Checklist for author

• npm run lint passes
• References to standard library functions are cached.

[fatso83]

To me, this looks fine, and I don't immediately see the reason to retroactively fix this in the previous versions, since it's not a bug.

[mroderick]

Thank you :)