Adding more details for how to build and test for the corefx repo

CONTRIBUTING.md

@@ -1,3 +1,22 @@
 # Contributing
 
-Information on contributing is in the [Contributing Guide](https://github.com/Microsoft/dotnet/blob/master/CONTRIBUTING.md).
+General information on contributing to dotnet projects is in the [Contributing Guide](https://github.com/Microsoft/dotnet/blob/master/CONTRIBUTING.md). This document contains information about coding styles, source structure, making pull requests, and more.
+
+# Contributing to the corefx repo
+
+## Required Software
+
+* Install [Visual Studio 2013 Desktop Express with Update 3](http://www.microsoft.com/en-us/download/details.aspx?id=43733) or Visual Studio 2015 Community Preview.
+
+## Building
+
+* Open a [Visual Studio Command Prompt](http://msdn.microsoft.com/en-us/library/ms229859(v=vs.110).aspx).
+* From the root of the repository, type `build`. This will build everything and run the core tests for the project.
+* Visual Studio Solution (.sln) files exist for related groups of libraries. These can be loaded in Visual Studio and run builds from within Visual Studio.
+
+## Testing
+
+* By default, the core tests are run as part of the build. A test report for the build will be output on the console at the end of a successful build.
+* To view and run the tests for a solution in Visual Studio you need to install **xUnit.net runner for Visual Studio**.
+	* In Visual Studio under `Tools->Extensions and Updates`, select `Online` on the left side and search for `xUnit`. Download the **xUnit.net runner for Visual Studio**.
+	* After downloading and restarting Visual Studio and building the test assemblies, the tests should start to show up in Test Explorer.