Add proxy support for ICMP echo request

docs/configuration/route/rule_action.md

@@ -2,6 +2,10 @@
 icon: material/new-box
 ---
 
+!!! quote "Changes in sing-box 1.13.0"
+
+    :material-alert: [reject](#reject)
+
 !!! quote "Changes in sing-box 1.12.0"
 
     :material-plus: [tls_fragment](#tls_fragment)  
@@ -42,6 +46,10 @@ See `route-options` fields below.
 
 ### reject
 
+!!! quote "Changes in sing-box 1.13.0"
+
+    Since sing-box 1.13.0, you can reject (or directly reply to) ICMP echo (ping) requests using `reject` action.
+
 ```json
 {
   "action": "reject",
@@ -58,9 +66,17 @@ For non-tun connections and already established connections, will just be closed
 
 #### method
 
+For TCP and UDP connections:
+
 - `default`: Reply with TCP RST for TCP connections, and ICMP port unreachable for UDP packets.
 - `drop`: Drop packets.
 
+For ICMP echo requests:
+
+- `default`: Reply with ICMP host unreachable.
+- `drop`: Drop packets.
+- `reply`: Reply with ICMP echo reply.
+
 #### no_drop
 
 If not enabled, `method` will be temporarily overwritten to `drop` after 50 triggers in 30s.