git-merge: show usage if run without arguments

diff --git a/delta.h b/delta.h
index 727ae30e9eb973b2bd4a512be78041fee40fa039..7b3f86d85f71e47d11c40a4abbcd9d9f499a6636 100644 (file)
--- a/delta.h
+++ b/delta.h
@@ -18,6 +18,8 @@ create_delta_index(const void *buf, unsigned long bufsize);
 
 /*
  * free_delta_index: free the index created by create_delta_index()
+ *
+ * Given pointer must be what create_delta_index() returned, or NULL.
  */
 extern void free_delta_index(struct delta_index *index);