What's missing in the contributing documentation? #5693

A new example section explaining on how to go about making a rule auto-fixable. This would include, but not limited to, the following:

• Using the checker.patch(...) method to check if the user wants to generate the patch which involves importing the AsRule trait:

   use crate::registry::AsRule;
   
   pub fn check_rule() {
   	// ...
   	let mut diagnotic = Diagnostic::new(...)
   	if checker.patch(diagnostic.rule.kind()) {
   		// ...
   	}
   	checker.diagnostics.push(diagnostic)
   }

• Types of Edit (insertion, deletion, replacement and their ranged variant)

• Setting the Applicability

• Generating the edits using:

  • libcst
  • Using the generator API (checker.generator().expr(...), checker.generator().stmt(...))
  • Manually generating the source string

• ...