docs(prefer-observer): when not to use it

Author: JasonWeinzierl

docs/rules/prefer-observer.md

@@ -49,6 +49,18 @@ This rule accepts a single option which is an object with an `allowNext` propert
 }
 ```
 
+## When Not To Use It
+
+If you rely on RxJS's deprecation of separate handlers and don't need to double-flag usage,
+then you don't need this rule.
+
+Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting.
+
 ## Further reading
 
 - [Subscribe Arguments](https://rxjs.dev/deprecations/subscribe-arguments)
+
+## Resources
+
+- [Rule source](https://github.com/JasonWeinzierl/eslint-plugin-rxjs-x/blob/main/src/rules/prefer-observer.ts)
+- [Test source](https://github.com/JasonWeinzierl/eslint-plugin-rxjs-x/blob/main/tests/rules/prefer-observer.test.ts)