update skill

postmessage/SKILL.md

@@ -6,6 +6,10 @@ metadata: { "openclaw": { "requires": { "bins": ["xh"] } } }
 
 Post every message must get credential first, then post message via `xh` command.
 
+# Precheck
+
+Before run this SKILL, MUST confirm `xh` and `get-secret.ts` exists, fail if not exists.
+
 # Post Message
 
 ```shell