Add vcpkg installation instructions (#211)

Author: JonLiu1993

README.md

@@ -128,6 +128,18 @@ $ touch WORKSPACE # declare that to be our workspace root
 $ bazel build gemmlowp:all
 ```
 
+### Building gemmlowp - Using vcpkg
+
+You can download and install gemmlowp using the [vcpkg](https://github.com/Microsoft/vcpkg) dependency manager:
+
+    git clone https://github.com/Microsoft/vcpkg.git
+    cd vcpkg
+    ./bootstrap-vcpkg.sh
+    ./vcpkg integrate install
+    ./vcpkg install gemmlowp
+
+The gemmlowp port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please [create an issue or pull request](https://github.com/Microsoft/vcpkg) on the vcpkg repository.
+
 ## Testing
 
 ### Testing by manually building and running tests