Added a file for bind mounts

Uptime-Kuma/.env.example

@@ -1,2 +1,5 @@
 # Host port that maps to Uptime Kuma's internal port 3001
 UPTIME-KUMA_PORT=3001
+
+# Linux username used to resolve the bind mount path (/home/<username>/uptime-kuma/data) — bind mount compose file only
+UPTIME-KUMA_USERNAME=