Docs for old supported versions should indicate that a newer version is available

I ended up on the [Django 2.2 version](https://docs.djangoproject.com/en/2.2/intro/tutorial01/) of the "Writing your first app" tutorial via web search, and didn't realize I was looking at outdated docs until I noticed the URL a few pages in. I realize that 2.2 [is still getting extended support](https://www.djangoproject.com/download/#supported-versions), but regardless this probably isn't the version of the tutorial that most people want, and the design of the page gives no indication that you're not looking at the latest version. Completely unsupported docs like [those for 1.8](https://docs.djangoproject.com/en/1.8/intro/tutorial01/) have a helpful banner at the top of the page indicating that the version isn't supported. I'm not saying a big scary red banner is necessary for old versions that are still supported, but some indication that there are newer versions would be nice.

This is a problem that a lot of projects face and solve in different ways - some examples below.

Examples of how other projects deal with this

- Postgres has a prominent version switcher at the top of every docs page indicating what versions are supported, plus a warning when you're looking at an unsupported version:


- Docs sites that use Read The Docs have a nice little "there is a newer version available" note at the top of outdated pages:


- CockroachDB provides an explicit warning on docs for old versions to indicate when they will stop being supported: