Add support section to the contributing guide

[Sander3003]

As a (potential) user/developer,
I would like to know where to find support for LF energy CoMPAS
So I can ask help

Add support information to SUPPORT: see https://com-pas.github.io/contributing/ to be refered to in the SUPPORT files in the different repositories.

Acceptance criteria:
Voluntary support channels: LF energy slack, Github issues
Professional services: Companies who can provide commercial support
Ask if Bearingpoint/SprintEins want to be on the list.

[Sander3003]

@david-monichi @trusz will you guys be on the list of commercial support providers?

[david-monichi]

More then happy to be part of it, thx