Clearly state which draft(s) of the JSON Schema specs is/are officially supported/targetted

**Is your feature request related to a problem? Please describe.**
This is not really a *feature* request per se, but it would be nice if it is clearly stated somewhere in the documentation or README, which draft(s) of the JSON Specification is officially supported or targetted. As far as I know, draft 4 and draft 7 are the most popular drafts that people want to use.

Given that the validation is delegated to Ajv, I would guess that draft 7 is supported as far as _validation_ is concerned. But how about the _form generation_ aspect?

I think a clear statement of the targetted draft(s) is useful for developers to pick the most suitable JSON editor for their purposes. It's good to have a clear starting point about expectations, even though we all know that there can be bugs or missing features.

**Describe the solution you'd like**
Clearly state, in the FAQ or README, which draft(s) of the JSON Schema specs is/are officially supported/targetted, optionally with a list of known issues relative to the drafts.

**Describe alternatives you've considered**
Try out jsonforms until I bump into issues myself and *guess* which draft I should expect to work.