Maybe add upgrade instructions

[ralfbiedert]

Documentation issue

Summary

It would be nice if Zola had upgrade instructions between version.

I just tried to compile my site with 0.16.1, but noticed that Markdown wouldn't render. I then spent some time reading previous release notes but couldn't find anything.

Now I'm not sure if there is a bug, or if something changed on purpose.

Proposed solution

Maybe add an UPGRADING.md to Github, which lists common pitfalls between "major" (i.e., 0.x to 0.y for prerelease) versions.

Edit - Ah, just realized it's because I have to rename .html shortcodes to .md (I could swear this has happened before and I fixed it), but anyhow, I was still looking for upgrade instructions when I didn't immediately grok what's wrong.

[Keats]

I try to put it in https://github.com/getzola/zola/blob/master/CHANGELOG.md in the breaking section but it's easy to miss some