Document the data model and testing workflow

[tordans]

To make it easier to contribute …

a. it would be great to have a documentation of the data model for the json.

Eg the "required:true" attribute is interesting, what does it "do" / how are clients supposed to use/interpret it?

b. it would be great to have a documentation about how to test a PR.

Eg is the only way to test this to create a local iD Editor instance and run it against a local copy? How would I do this? Or is there maybe a version of iD Editor that allows testing of manually pasted JSON files?

Thanks

Update:

• "best" is described at Explore improvements to "best" flag #130 (comment)

  Consider "best" as meaning "better than Bing according to local mappers".

• "required" is described at Change tile server for berlin images #515 (comment) ""

  an editor is required to show the attribution line

[bhousel]

a. it would be great to have a documentation of the data model for the json.

The JSON-Schema doc https://github.com/osmlab/editor-layer-index/blob/gh-pages/schema.json is both the data model and the documentation.

[tordans]

Fore Reference: #562