added windows to INSTALL.md

INSTALL.md

@@ -55,3 +55,55 @@ gRPC C Core library.
  $ make
  $ [sudo] make install
 ```
+
+##Windows
+
+There are several way to build under Windows, of varying complexity depending on
+experience with the tools involved.
+
+<!--
+###Visual Studio
+
+Versions 2013 and 2015 are both supported. You can use [their respective
+community
+editions](https://www.visualstudio.com/en-us/downloads/download-visual-studio-vs.aspx).
+
+Building the C Core:
+- Open [grpc.sln](https://github.com/grpc/grpc/blob/master/vsprojects/grpc.sln).
+- Select your build target.
+- Build the `grpc` project.
+
+Building the C++ runtime:
+- You need [CMake](https://cmake.org/) on your path to build protobuf (see below
+  for building using solely CMake).
+- Run `vsprojects/build_protos.bat` (needs `cmake.exe` in your path).
+- Open [buildtests_cxx.sln]()
+- Select your build target.
+- build the `grpc++` project.
+-->
+
+###msys2
+
+This approach requires having [msys2](https://msys2.github.io/) installed.
+
+- The Makefile (and source code) should support msys2's mingw32 and mingw64
+  compilers. Building with msys2's native compiler is also possible, but
+  difficult.
+- The Makefile is expecting the Windows versions of OpenSSL (see
+  https://slproweb.com/products/Win32OpenSSL.html). It's also possible to build
+  the Windows version of OpenSSL from scratch. The output should be `libeay32`
+  and `ssleay32`.
+- If you are not installing the above files under msys2's path, you may specify
+  it, for instance, in the following way:
+  ```CPPFLAGS=”-I/c/OpenSSL-Win32/include” LDFLAGS=”-L/c/OpenSSL-Win32/lib” make static_c```
+- [protobuf3](https://github.com/google/protobuf/blob/master/src/README.md#c-installation---windows)
+  must be installed on the msys2 path.
+
+###Cmake (experimental)
+
+- Install [CMake](https://cmake.org/download/).
+- Run it over [grpc's
+  CMakeLists.txt](https://github.com/grpc/grpc/blob/master/CMakeLists.txt) to
+  generate "projects" for your compiler.
+- Build with your compiler of choice. The generated build files should have the
+  protobuf3 dependency baked in.