docs: Add user-friendly guide about how to use ws_server_example_test.py

examples/protocols/http_server/ws_echo_server/README.md

@@ -6,7 +6,8 @@ This example demonstrates the HTTPD server using the WebSocket feature.
 ## How to Use Example
 
 The example starts a WS server on a local network, so a WS client is needed to interact with the server (an example test
-ws_server_example_test.py could be used as a simple WS client).
+ws_server_example_test.py could be used as a simple WS client). If you run ws_server_example_test.py and get
+`ModuleNotFoundError: No module named 'websocket'`, then please install `websocket` by running `python -m pip install websocket-client`.
 
 The server registers WebSocket handler which echoes back the received WebSocket frame. It also demonstrates
 use of asynchronous send, which is triggered on reception of a certain message.

examples/protocols/http_server/ws_echo_server/ws_server_example_test.py

@@ -20,9 +20,14 @@ import os
 import re
 
 import ttfw_idf
-import websocket
 from tiny_test_fw import Utility
 
+try:
+    import websocket
+except ImportError:
+    print("Please install 'websocket' by running 'python -m pip install websocket-client'")
+    raise
+
 OPCODE_TEXT = 0x1
 OPCODE_BIN = 0x2
 OPCODE_PING = 0x9