Add to contributing file some development directives

[palladius]

Hi all, would be nice that all the tests done in the CI where somewhat documented in the contrib file. Even better to DRY it in code, eg a simple test . I'm updating a local justfile with these 2 commands:

    bundle exec erblint --lint-all
    standardrb --fix

and God knows if I'm done with testing :) Would be great to just run some local testing command to go through all of it, so if it passes the tests locally there's a good chance it passes them in CI too.

[marcoroth]

Maybe it's not quite what you are looking for, but we have a bin/lint executable you can run:

https://github.com/rubyevents/rubyevents/blob/main/bin/lint