README: admonition

Signed-off-by: lucasew <[email protected]>

README.md

@@ -26,7 +26,7 @@ version! It's as safe and stable as
 [tclip](https://github.com/tailscale-dev/tclip) is because this proxy uses the
 exact same primitives.
 
-> [!WARNING] About header authentication security
+> [!WARNING]
 > You can count on the headers sent by ts-proxy as long as you follow the following conditions:
 > - Anything that changes the headers name representation such as Apache with PHP could be cheated
 > by passing the header TAILSCALE_USER_LOGIN, for example.