add English-only requirement to skill docs

claw-skills/workflows/improve-skills.md

@@ -10,6 +10,13 @@ Used when a skill or workflow has one of these problems:
 
 Improvement is better than workaround. Fix problems when you find them, so others don't hit the same坑.
 
+## Requirement
+
+**All skill-related documentation must be written in English.** This applies to:
+- Creating new skills or workflows
+- Improving or correcting existing skills
+- Any other documentation within skills
+
 ## Process
 
 ### 1. Identify the Problem