Update Documentation to reflect V2 changes

[larskristianhaga]

The V2 action was released in October 2023, and the documentation is still referring to V1 of the GitHub Action.

[martgra]

+1 to this. also better description of how to use yaml. I find some bits and pieces here and there regarding the $VARIABLE_NAME$ syntax from the example files but would be great to understand how its thought to be used.

[felipementel]

Can anyone tell me why this pull request has not been accepted yet?