DOC: Link to paper in README.

README.md

@@ -2,10 +2,18 @@
 
 A collection of tools that one can use to reason with GATs and organize models of GATs.
 
-# Features
+## Features
 
 - Declaration of GATs
 - Multiple inheritance of GATs via pushouts
 - Parameterized models of GATs ala Standard ML modules/functors
 - E-Graph backed rewriting and type inference in arbitrary GATs
 - Backwards compatibility with the Catlab implementation of GATs
+
+## Further reading
+
+The design and essential features of GATlab are described in our paper:
+
+> O. Lynch, K. Brown, J. Fairbanks, E. Patterson, 2024:
+> "GATlab: Modeling and Programming with Generalized Algebraic Theories"
+> [arXiv:2404.04837](https://arxiv.org/abs/2404.04837)