docs: use a real generated secret in coturn example

Replace placeholder YOUR_RANDOM_SECRET with an actual openssl rand -hex 32
output, with a note to generate a fresh one. Keeps the example copy-pasteable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -104,12 +104,18 @@ apt install coturn
 listening-port=3478
 fingerprint
 use-auth-secret
-static-auth-secret=YOUR_RANDOM_SECRET
+static-auth-secret=b06c504fd091d23c1ae3699337259d7883a0af1c72fe782044de19f314a267aa
 realm=your-domain.com
 no-tcp-relay
 ```
 
-Replace `YOUR_RANDOM_SECRET` with any random string (e.g. `openssl rand -hex 32`). Enable and start:
+Generate your own secret (do not reuse the example above):
+
+```bash
+openssl rand -hex 32
+```
+
+Enable and start:
 
 ```bash
 systemctl enable coturn
@@ -122,7 +128,7 @@ systemctl start coturn
 window.WASTE_CONFIG = {
   signalURL: 'wss://your-domain.com/ws',
   turnURL: 'turn:your-domain.com:3478',
-  turnSecret: 'YOUR_RANDOM_SECRET',
+  turnSecret: 'b06c504fd091d23c1ae3699337259d7883a0af1c72fe782044de19f314a267aa',
 }
 ```