Add admonitions marking community-provided docs

docs/reverse-proxy.md

@@ -1,5 +1,12 @@
 # Running headscale behind a reverse proxy
 
+!!! warning "Community documentation"
+
+    This page is not actively maintained by the headscale authors and is
+    written by community members. It is _not_ verified by `headscale` developers.
+
+    **It might be outdated and it might miss necessary steps**.
+
 Running headscale behind a reverse proxy is useful when running multiple applications on the same server, and you want to reuse the same external IP and port - usually tcp/443 for HTTPS.
 
 ### WebSockets