clone: print advice on checking out detached HEAD

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/advice.h b/advice.h
index e5d0af7..7bda45b 100644
--- a/advice.h
+++ b/advice.h
@@ -14,5 +14,6 @@
 void advise(const char *advice, ...);
 int error_resolve_conflict(const char *me);
 extern void NORETURN die_resolve_conflict(const char *me);
+void detach_advice(const char *new_name);
 
 #endif /* ADVICE_H */