Add Traefik prefix to the KV key

docs/user-guide/kv-config.md

@@ -148,6 +148,37 @@ This variable must be initialized with the ACL token value.
 
 If Traefik is launched into a Docker container, the variable `CONSUL_HTTP_TOKEN` can be initialized with the `-e` Docker option : `-e "CONSUL_HTTP_TOKEN=[consul-acl-token-value]"`
 
+If a Consul ACL is used to restrict Træfik read/write access, one of the following configurations is needed.
+
+- HCL format :
+
+```
+    key "traefik" {
+        policy = "write"
+    },
+    
+    session "" {
+        policy = "write"
+    }
+```
+
+- JSON format :
+
+```json
+{
+    "key": {
+        "traefik": {
+          "policy": "write"
+        }
+    },
+    "session": {
+        "": {
+        "policy": "write"
+        }
+    }
+}
+```
+
 ### TLS support
 
 To connect to a Consul endpoint using SSL, simply specify `https://` in the `consul.endpoint` property