The CONTRIBUTING.md file states that our CI does not run regression
checks on Windows, which is outdated information. In fact, we do execute
regression checks on Windows in our current CI. This pull request
removes the outdated section.
We're not using Travis CI anymore and moved all our CI infrastructure
to Github Actions.
Replaced all old Travis CI mentioning to Github Actions on contributors
documentation.
Closes#3700
Since we require that commit messages follow seven rules of writing good
commit messages and include GitHub issues number, this commit clarifies these
requirements in the contribution.
