Create contribute.json

Unneeded comma at the end of this line. Please validate your file against the schema after making changes as there are a few syntax issues like this. You can use `json-schema-validator` [1] with the contribute.json schema [2] to validate it.

[1] https://json-schema-validator.herokuapp.com/
[2] https://github.com/mozilla/contribute.json/blob/master/schema.json