message: docs: Fix heading levels
  Markdown headings cannot be too high-level lest they render incorrectly
  in the docs app.
diff: @@ -121,7 +121,7 @@ export class Observable<T> implements Subscribable<T> {
  * by default emits all its values synchronously. Always check documentation for how given Observable
  * will behave when subscribed and if its default behavior can be modified with a `scheduler`.
  *
  - * ## Examples
  + * #### Examples
  *
  * Subscribe with an {@link guide/observer Observer}
  *
  @@ -261,7 +261,7 @@ export class Observable<T> implements Subscribable<T> {
  * this situation, look into adding something like {@link timeout}, {@link take},
  * {@link takeWhile}, or {@link takeUntil} amongst others.
  *
  - * ## Example
  + * #### Example
  *
  * ```ts
  * import { interval, take } from 'rxjs';
  