[Docs] Update check commands in Japanese documents (#7787)

The Japanese documents included a sample command to check the original document changes. But there was something wrong, so I fixed it.

docs/ja/faq_general.md

@@ -2,7 +2,7 @@
 
 <!---
   original document: d598f01cb:docs/faq_general.md
-  git diff d598f01cb HEAD docs/faq_general.md | cat
+  git diff d598f01cb HEAD -- docs/faq_general.md | cat
 -->
 
 ## QMK とは何か？