Update README to list "features" of S3 connector

[chipmaurer]

I came up with these features. Please add comments for updates

• Generic S3 object store queries (hive not required)
• Tested on Dell Technologies Elastic Cloud Storage (ECS), Scality CloudServer and MinIO Object Storage Server
• Supports CSV, JSON, Parquet and Avro input
• Snappy and gzip compressed files
• Create table support (CSV and JSON), including 'Create Table AS'
• Uses Dell Schema Registry for dynamic table creation, but also supports static configuration of tables using JSON configuration files

[fpj]

We might want to mention explicitly that we use the AWS S3 client. I'm also thinking that we should mention the S3 Select support.

"Dell Schema Registry" is the Pravega schema registry, right? https://github.com/pravega/schema-registry