Time for release notes

[Dridi Boukelmoune]

Dear Varnish developers,

It's that time of the semester already, the time where we all enjoy
revisiting what happened in the last 6 months to produce release and
upgrade notes.

As such I'll spend the rest of today and tomorrow trying to make
progress on 6.3 documentation.

At this point you might think "wait a minute the next release is 6.4"
and you would be right but it turns out we didn't wrap up that
documentation before last September release.

As I'm going to revisit the 6.3 release, motivated contributors may
start filling up the skeleton for the upcoming 6.4 release so that I
don't run into conflicts and can be done faster and eventually
back-port the missing bits to the 6.3 branch.

Thanks,
Dridi

PS. I'm not pointing fingers, I also let it slip