Update readme with additional resource link

Added a link to the barcode cheatsheets repository.

Author: arran4

readme.md

@@ -2,4 +2,6 @@
 
 ![vim-barcodes-a4.png](vim-barcodes-a4.png)
 
-Most of these barcodes are place holders until I think of something better to put there.
+Most of these barcodes are place holders until I think of something better to put there.
+
+See https://github.com/arran4/barcode-cheatsheets for more