Add a documentation page about updating to the latest WordPress security release

[johnbillion]

As a user of Altis Cloud I want to quickly find out how to update to the latest WordPress security release so I can deploy the update without delay.

There appears to be no information in the docs for this specific workflow. Fundamentally composer update altis/altis -W achieves this, but this can also pull in many other dependency updates. In order to narrow the updates, composer update altis/cms -W might be preferred. The effect this has is updating the johnpbloch/wordpress package to the latest patch release.

Let's create a page for this.