Fix README.

README.md

 ## Introduction
 
-Files from the [Purdue Reactive Molecular Dynamics][https://www.cs.purdue.edu/puremd] (PuReMD) project.
+Files from the [Purdue Reactive Molecular Dynamics](https://www.cs.purdue.edu/puremd) (PuReMD) project.
 
 ## Relevant Papers
 
 Roughly by target platform
-- [Single core][https://www.cs.purdue.edu/puremd/docs/80859.pdf] (serial)
-- [Distributed memory][https://www.cs.purdue.edu/puremd/docs/Parallel-Reactive-Molecular-Dynamics.pdf] (message passing interface)
-- [Massively multithreaded][http://dx.doi.org/10.1016/j.jcp.2014.04.035] (single GPU)
-- [Massively multithreaded][https://www.cs.purdue.edu/puremd/docs/pgpuremd.pdf] (multi-GPU)
+- [Single core](https://www.cs.purdue.edu/puremd/docs/80859.pdf) (serial)
+- [Distributed memory](https://www.cs.purdue.edu/puremd/docs/Parallel-Reactive-Molecular-Dynamics.pdf) (message passing interface)
+- [Massively multithreaded](http://dx.doi.org/10.1016/j.jcp.2014.04.035) (single GPU)
+- [Massively multithreaded](https://www.cs.purdue.edu/puremd/docs/pgpuremd.pdf) (multi-GPU)