Add ref card.

README.md

@@ -588,6 +588,9 @@ For the string library, there is for example:
 API Documentation
 -----------------
 
+The M*LIB reference card is available [here](https://github.com/P-p-H-d/mlib/blob/master/doc/Container.html).
+
+
 ### M-LIST
 
 This header is for creating [singly linked list](https://en.wikipedia.org/wiki/Linked_list).