Pitfall section in readme.md for newcomers (#111)

Co-authored-by: Artur Androsovych <[email protected]>

README.md

@@ -155,6 +155,11 @@ You can use `--removeOnDestroy` flag for empty `OnDestroy` methods removing.
 npx @ngneat/until-destroy --removeOnDestroy
 ```
 
+## Potential Pitfalls
+
+- The order of decorators is important, make sure to put `@UntilDestroy()` before the `@Component()` decorator.
+- When using [`overrideComponent`](https://angular.io/api/core/testing/TestBed#overrideComponent) in unit tests remember that it overrides metadata and component definition. Invoke `UntilDestroy()(YourComponent);` to reapply the decorator. See [here](https://github.com/ngneat/until-destroy/issues/91#issuecomment-626470446) for an example.
+
 ## Contributors ✨
 
 Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/docs/en/emoji-key)):