screen19 now supports DIALS 3 and DIALS 2.2.

`DIALS is available here <https://dials.github.io/installation.html>`_.

* DIALS 3 is the latest major release and is actively supported.  It is currently Python 3.6 only.
* DIALS 2.2 is a long-term support release.  It only receives bug fixes and support will be withdrawn at the end of 2020.  It supports Python 2.7 and 3.6.
* DIALS 1.14 is no longer under active development and screen19 support for it has been withdrawn.

Add news about DIALS versions supported
Add news about DIALS versions supported
