Add README.md to Python API Gateway WebSocket example
Add README.md to Python API Gateway WebSocket example

Merge pull request #757 from awsdocs/py_websocket_readme
awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples,awsdocs/aws-doc-sdk-examples