4.0.x changelog items

Very much appreciate what you're doing here. A couple of minor items:

• The changelog link on README.md is incorrect ('changelog' in the link needs to be uppercase)
• The changelog itself seems to be lagging the latest 4.0.x release(s). After digging, I found some info on the Migration wiki page, but unsure what other changes have taken place.

[dkunzler]

Hi, thanks for the hints.
Unfortunately documentation is the one thing this project is lacking. Still missing pages in the wiki...

I updated the changelog and the link to the changelog now!