Add official builds download link

README.md

@@ -26,6 +26,8 @@ NCCL requires at least CUDA 7.0 and Kepler or newer GPUs. For PCIe based platfor
 
 ## Build
 
+Note: the official and tested builds of NCCL can be downloaded from: https://developer.nvidia.com/nccl. You can skip the following build steps if you choose to use the official builds.
+
 To build the library :
 
 ```shell