Add GRPC build instructions to readme

README.md

@@ -12,3 +12,43 @@ $ pip install grpcio-tools gevent
 $ pip install grpcio # Need to install grpcio-tools first to avoid a versioning problem
 ```
 
+Building GRPC
+-------------
+
+In order to compile this project, and anything which depends on it, you will need a working installation
+of the GRPC C core libraries. This library currently uses the 0.14 version range, so checkout an appropriate revision
+of the repository, and install as follows:
+
+```sh
+git clone https://github.com/grpc/grpc.git
+git checkout 2b223977c13975648bac2f422363e1ebf83506ce
+cd grpc
+git submodule update --init
+make
+sudo make install
+```
+
+Alternatively, using Nix, pass the following expression to `nix-build` and point Stack to the build products in the Nix store:
+
+```nix
+let pkgs = import <nixpkgs> {};
+in  pkgs.stdenv.mkDerivation rec
+    {   name = "grpc";
+        src = pkgs.fetchgit
+        { url    = "https://github.com/grpc/grpc.git";
+          rev    = "2b223977c13975648bac2f422363e1ebf83506ce";
+          sha256 = "0arxjdczgj6rbg14f6x24863mrz0xgpakmdfg54zp0xp7h2pghm6";
+        };
+        preInstall = "export prefix";
+        buildInputs =
+        [   pkgs.darwin.cctools
+            pkgs.autoconf
+            pkgs.automake
+            pkgs.libtool
+            pkgs.which
+            pkgs.zlib
+
+            pkgs.openssl
+        ];
+    }
+```