add more info for telemetry disable

Author: msukkari

docs/self-hosting/overview.mdx

@@ -123,4 +123,10 @@ docker run \
   -e SOURCEBOT_TELEMETRY_DISABLED=true \
   /* additional args */ \
   ghcr.io/sourcebot-dev/sourcebot:latest
+```
+
+If you disabled telemetry correctly, you'll see the following log when starting Sourcebot:
+
+```sh
+Disabling telemetry since SOURCEBOT_TELEMETRY_DISABLED was set.
 ```