Documentation: how to disable warnings and keep the codefix actions

[fsateler]

I have a relatively old and relatively large codebase. I have disabled the CSE0003 warning because of the large amount of occurrences, but I change them manually whenever I edit the vicinity of the code. It would be very handy if the Ctrl+. action item did not disappear when the warning is supressed.

The documentation did not hint that I could use a Ruleset file to lower the warning level into hidden. This prevents the display of warnings while keeping the codefix actions.

I tried this idea after reading the SonarLint FAQ, which pointed me to the ruleset file. I think a similar section should be added to the readme.