Severity level definition

[emmuhamm]

Description

Fixes #56

Add the definition of severity levels for other people to use in the DUNE DAQ.

Its a separate PR cuz I'm sure this needs a wider discussion before we can agree to this.

Type of change

• Documentation (non-breaking change that adds or improves the documentation)

Testing checklist

N/A

Further checks

N/A

[PawelPlesniak]

It is good to have this written down as a reference point. Some requests. In your example, you use Bad query for logs as an example of an ERROR message, but it is a WARNING message. A better example would be when we have the web proxy enabled.

Also for the CRITICAL example, lets stick to things that relate to our work that is publishable through python. The example you provided relates to a C++ app. I would suggest using "A process died unecpectedly" instead.