real_path: clarify return value ownership

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

abspath.c

@@ -202,6 +202,10 @@ error_out:
 	return retval;
 }
 
+/*
+ * Resolve `path` into an absolute, cleaned-up path. The return value
+ * comes from a shared buffer.
+ */
 const char *real_path(const char *path)
 {
 	static struct strbuf realpath = STRBUF_INIT;