Clean up build guide links (#71):

- Remove _Nixpkgs
- Move _patch-fsharp-targets to default.nix
- Add link for MONO_PATH

default.nix

@@ -6,7 +6,13 @@ with import <nixpkgs> {}; rec {
   naggumEnv = stdenv.mkDerivation {
     name = "naggum";
     buildInputs = [ mono fsharp dotnetPackages.Nuget ];
+
+    # For more info regarding this variable see:
+    # https://github.com/NixOS/nixpkgs/blob/d4681bf62672083f92545e02e00b8cf040247e8d/pkgs/build-support/dotnetbuildhelpers/patch-fsharp-targets.sh
     FSharpTargetsPath="${fsharp}/lib/mono/${frameworkVersion}/Microsoft.FSharp.Targets";
+
+    # For more info regarding this variable see:
+    # http://www.mono-project.com/docs/advanced/assemblies-and-the-gac/
     MONO_PATH="${fsharp}/lib/mono/Reference Assemblies/Microsoft/FSharp/.NETFramework/v${fsharpVersion}/${assemblyVersion}/";
   };
 }

docs/build-guide.rst

@@ -58,8 +58,6 @@ html`` (on Linux) or ``.\make.bat html`` (on Windows).
 .. _F# Compiler: http://fsharp.org/
 .. _Mono: http://www.mono-project.com/
 .. _NixOS Linux: http://nixos.org/
-.. _Nixpkgs: https://github.com/NixOS/nixpkgs
 .. _NuGet: http://www.nuget.org/
-.. _patch-fsharp-targets:  https://github.com/NixOS/nixpkgs/blob/d4681bf62672083f92545e02e00b8cf040247e8d/pkgs/build-support/dotnetbuildhelpers/patch-fsharp-targets.sh
 .. _Python: https://www.python.org/
 .. _Sphinx: http://sphinx-doc.org/