Add Shortbread style JSON URLs

[gy-mate]

In order to make setting it up in QGIS (for personal use) easier.

Also:

• change the zoom variable to z as required by QGIS
• fix grammar.

[pnorman]

I'm reluctant to imply long-term support for the internal style URL. It commits us to continuing to host the specific style long term while we've only done that for the vector tiles.

Also, the style URL is wrong - it's not $VERSION (e.g. shortbread_v1), it's the style name.

If we do publish the style URL it should be a separate paragraph and recommend people host the style themselves. That way they won't get surprised by style changes that don't work with whatever they're doing with the map.

[gy-mate]

That's a good point!

Is it okay this way?

[pnorman]

That's a good point!

Is it okay this way?

We still haven't decided on a policy in openstreetmap/operations#1263. Once that is decided we'll know what the URLs are, if any.

[gy-mate]

Sure, thanks! :)