Draft for mail about ci

[Halla Rempt]

Sorry for the delay... Here's my first draft, please reply with suggestions and corrections.


Cheers,

Halla
-------------
The situation: Krita has a lot of *complicated* and *new* dependencies. Some dependencies need to be patched if the result is to be a working Krita, and some aren't available on distributions yet. We're also moving quite fast when it comes to updating and fixing dependencies -- and even upstreaming fixes.

This gives the following problem:

* Jenkins CI depends, afaik, on distribution packages for dependencies. While it's important that Krita builds on distributions, that doesn't produce a version of Krita or a unittest run that works for Krita developers.
* We need a CI that builds against our dependencies so we can have artefacts and unittest runs that represent our intention.
* And we also still need release and nightly builds, not just builds after merging an MR

I'm not sure how we can solve the problem of missing or outdated dependencies on distribution CI: should we make an external cmake project that builds those as part of the main build system?
-------------