Document how to get exit code in build scripts

**Is your feature request related to a problem? Please describe.**
Our build script on Azure Devops do not stop even if Grate has a problem. I think Grate returns -1 or 1 as an exit code but it looks like "dotnet run grate" does not forward this exit code to the Powershell script that Devops is using.

**Describe the solution you'd like**
Please add some documentation of how to make this work in the most common build system. Azure Devops for me but I assume Github actions would also be a good idea. If the solution is to not use "dotnet run" then there should be documentation showing to to do some other method and if possible add some explanation why this is useful.

**Describe alternatives you've considered**
Just building a Grate binary and call that directly.