Request to add supported options list in README

[shsachin]

This is not an issue. It is a request to improve README documentation. I am not sure where do I put it.

spark-csv #Features says : API accepts several options. A list of accepted options is followed with brief description. This is very intuitive to understand supported options.

Can we please have such a list for spark-avro as well. I know it is mentioned in README but it looks scattered and is not like a list.