Update link to PPoPP paper

README.md

@@ -7,7 +7,7 @@ benchmark suite to test the compiler infrastructure.
 
 ## Paper
 
-[PPoPP'18 paper](http://rsim.cs.illinois.edu/Pubs/17-PPOPP-HPVM.pdf)
+[PPoPP'18 paper](https://dl.acm.org/doi/pdf/10.1145/3200691.3178493)
 
 ## Docs
 [HPVM IR Specification](/hpvm/docs/hpvm-specification.md)
@@ -23,7 +23,7 @@ The following components are required to be installed on your machine to build H
 * CMake (>=3.4.3)
 * Python (>=2.7)
 * GNU Make (>=3.79.1)
-* CUDA 9.1 (only required for GPU support)
+* CUDA (>= 9.1) (only required for GPU support)
 
 ## Getting source code and building HPVM