Update CHANGELOG

[sj26]

The changelog seems to be missing entries since 2.6.0:

https://github.com/jch/html-pipeline/blob/master/CHANGELOG.md

What's changed?

[gjtorikian]

I'm pretty much the only maintainer here, and I don't have the time or energy to implement some kind of automation for this, I'm sorry to say.

It's probably not super user-friendly, but I tag every release, and you can look at the diff between releases to identify any minor/patch changes.

[sj26]

No worries, maybe I can help :-)

#316