Add tutorial to add-on store to quick start guide

[seanbudd]

Is your feature request related to a problem? Please describe.

The add-on store is documented in the user guide, which is primarily a reference material.
As managing add-ons is relatively complex for new users, and important for the new user experience, there should be tutorial materials available.

Describe the solution you'd like

The quick start guide is a basic tutorial which is perfect for this documentation.
We can also add this to Basic Training for more advanced and detailed discussion.

Good base for this: https://github.com/nvaccess/nvda/blob/master/tests/manual/addonStore.md

Describe alternatives you've considered

As is

Additional context

[seanbudd]

Closed by #16553