extend doc related to https://github.com/Kozea/Radicale/issues/1804

DOCUMENTATION.md

@@ -763,6 +763,8 @@ The maximum size of the request body. (bytes)
 
 Default: `100000000`
 
+In case of using a reverse proxy in front of check also there related option
+
 ##### timeout
 
 Socket timeout. (seconds)

config

@@ -22,6 +22,7 @@
 #max_connections = 8
 
 # Max size of request body (bytes)
+# In case of using a reverse proxy in front of check also there related option
 #max_content_length = 100000000
 
 # Socket timeout (seconds)