Update 'backlog.md'

backlog.md

@@ -56,4 +56,5 @@
 - [Galerie Dada](https://www.galeriedada.com/)
 - [Simon's Algorithm](https://en.wikipedia.org/wiki/Simon%27s_problem)
 - [Galois Connection](https://en.wikipedia.org/wiki/Galois_connection)
-- [Groebner Basis](https://en.wikipedia.org/wiki/Gr%C3%B6bner_basis)
+- [Groebner Basis](https://en.wikipedia.org/wiki/Gr%C3%B6bner_basis)
+- [Nim](https://en.wikipedia.org/wiki/Nim)