The alert component docs were not clear at all on how to use a notification component that required something like `target` to function. The answer is to wrap it in a `group` notification component so this adds some documentation and examples on how to do that.
* Alert component documentation.
Added the documentation for the alert component.
home-assistant/home-assistant#5201
* Updated alert documentation to reflect changes made in PR.
* Bumped the ha_release number.
