Reinstate link to "Understanding JSON Schema"

[mdboom]

There was, at one time, a link to "Understanding JSON Schema" on json-schema.org.

Understandably, as it became out-of-date, it was removed. Now that it's moved to the json-schema-org and updates are underway, we should not forget to reinstate the link, once we all agree it's ready.

I leave it up to you whether that should be after the updates for Draft 6 go in, or after it gets updated all the way to Draft 7, which is currently blocked by Draft 7 support in the Python jsonschema library (but reportedly not for long).

[Relequestual]

I think it's fine to link back when draft-6 is done. A note can be added to the site that it only demonstrates draft-6, and one should view the changelog of draft-7.

At least, I'm OK with that.

[Julian]

Still some kinks to work out (please lemme know if you find any!) but just pushed out a first draft 7 alpha release (v3.0.0a3).

[handrews]

@Relequestual are we ready to re-link this?

[Relequestual]

@mdboom How are things looking? @handrews looks like https://github.com/json-schema-org/understanding-json-schema/issues/79 is still open. This would be the main indicator I believe.

[mdboom]

Draft 6 is done. I haven't started the Draft 7 work, but now that Python's jsonschema has support it should hopefully be smooth sailing.

[mdboom]

First round of Draft 7 changes are available in https://github.com/json-schema-org/understanding-json-schema/pull/84

[Relequestual]

Closing this issue as we have since ingested all the site content and include it as part of our reference documentation.