added Heuristic source (non-https)

README.md

@@ -25,3 +25,4 @@ This orientation allows all moves to be done with either a 7 bit or 1 bit rotati
 The vast majority of the project is personal work but there were some inspirations and little tricks from various sources. Any code directly copied from a source like StackOverflow is stated inline in comments. An exhaustive list of all sources used is here:
 * [Checkers Bitboard Tutorial](http://www.3dkingdoms.com/checkers/bitboards.htm#movegen)
 * [Compiler Friendly Bit Rotation in C](http://stackoverflow.com/questions/776508/best-practices-for-circular-shift-rotate-operations-in-c)
+* [Evolutionary-based heuristic generators](https://pdfs.semanticscholar.org/91c9/d140267f3b008d00b330b6b0e9182fa4b62e.pdf)