Add README.md to Python API Gateway WebSocket example

Author: SCalwas

python/example_code/apigateway/websocket/README.md

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+# AWS API Gateway WebSocket Chat Program
+
+## Repository files
+
+* `websocket.py` : Main program source file
+* `lambda_util.py` : Utility functions to manage AWS Lambda functions
+* `websocket_connect.py` : AWS Lambda function to implement the WebSocket `$connect` route
+* `websocket_disconnect.py` : AWS Lambda function to implement the WebSocket `$disconnect` route
+* `websocket_send_msg.py` : AWS Lambda function to implement the WebSocket `sendmsg` custom route (Python)
+* `websocket_send_msg.js` : AWS Lambda function to implement the WebSocket `sendmsg` custom route (JavaScript)
+
+## AWS infrastructure resources
+
+* API Gateway WebSocket API
+* AWS Lambda functions for the WebSocket `$connect` and `$disconnect` routes and a WebSocket `sendmsg` custom route
+* AWS Identity and Access Management (IAM) role and policy for the AWS Lambda functions
+* Amazon DynamoDB table to store connection IDs and user names
+
+## Prerequisites
+
+* Install Python 3.x.
+* Install the AWS SDK for Python `boto3`. Instructions are at https://github.com/boto/boto3.
+* Install the AWS CLI (Command Line Interface). Instructions are at 
+  https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-install.html.
+* Configure the AWS CLI. Instructions are at 
+  https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html.
+
+## Instructions
+
+To create the WebSocket infrastructure:
+
+    python websocket.py
+
+To delete the WebSocket infrastructure:
+
+    python websocket.py -d
+    OR
+    python websocket.py --delete
+
+To use the WebSocket Chat Program:
+
+1. Download and install `Node.js` from https://nodejs.org. `Node.js` includes the `npm` package manager.
+2. Use `npm` to globally install `wscat`.
+
+        npm install -g wscat
+
+3. When the WebSocket infrastructure is created, the WebSocket WSS address is output.
+   Copy the output WebSocket WSS address and enter it on the `wscat` command line to open
+   a WebSocket connection. Open multiple connections by running `wscat` in separate
+   terminal windows.
+   
+        wscat -c WSS_ADDRESS
+
+   Example command line:
+   
+        wscat -c wss://123abc456def.execute-api.us-west-2.amazonaws.com/dev
+
+   Optional: Specify a user name as a query parameter in the WSS address (Used
+   by the Python version of `websocket_send_msg.py`)
+   
+        wscat -c wss://123abc456def.execute-api.us-west-2.amazonaws.com/dev?name=Steven
+
+4. Send a chat message to all open connections:
+
+        {"action": "sendmsg", "msg": "Enter message text here"}
+
+   The `"action": "sendmsg"` pair invokes the WebSocket `sendmsg` custom route.
+   
+   The `"msg": "Enter message text here"` pair specifies the message text to send.
+
+5. To close the WebSocket connection:
+
+        <Ctrl-C>