Add readme.md to explain usage.

examples/supervisor/readme.md

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+# Supervisor Example
+
+This example demonstrates how to use the supervisor to detect memory leaks and respond to them.
+
+## `falcon.rb` Configuration
+
+The `falcon.rb` configuration file is used to configure the Falcon web server, along with the supervisor. We have a custom `MemoryMonitor` so we can override some of the behaviour when a memory leak is detected.
+
+## Usage
+
+First, start the Falcon web server with the supervisor:
+
+```bash
+$ bundle exec falcon host falcon.rb
+```
+
+Then, cause a server instance to leak memory:
+
+```bash
+$ bake leak
+```
+
+The supervisor will detect the memory leak and restart the server instance:
+
+```
+50.17s    error: Falcon::Configuration::Loader["falcon.rb"]::MemoryMonitor [oid=0x548] [ec=0x550] [pid=91808] [2025-03-01 12:43:04 +1300]
+               | Memory leak detected in process:
+               | {
+               |   "process_id": 91805,
+               |   "monitor": {
+               |     "process_id": 91805,
+               |     "current_size": 27279360,
+               |     "maximum_size": null,
+               |     "maximum_size_limit": 20971520,
+               |     "threshold_size": 10485760,
+               |     "increase_count": 0,
+               |     "increase_limit": 20
+               |   }
+               | }
+50.27s     info: Falcon::Configuration::Loader["falcon.rb"]::MemoryMonitor [oid=0x548] [ec=0x550] [pid=91808] [2025-03-01 12:43:04 +1300]
+               | Memory dumped...
+               | {
+               |   "response": {
+               |     "path": "memory-91805.json"
+               |   }
+               | }
+50.27s     info: Falcon::Configuration::Loader["falcon.rb"]::MemoryMonitor [oid=0x548] [ec=0x550] [pid=91808] [2025-03-01 12:43:04 +1300]
+               | Killing process:
+               | {
+               |   "process_id": 91805
+               | }
+```