Merge pull request #7668 from BobSilent/improve-contributing-md-for-windows-users

improve contributing.md for windows user

.github/CONTRIBUTING.md

@@ -63,7 +63,6 @@ POSIX-like environments (macOS, Linux, Cygwin, etc.) so you may need to
 adjust them for Windows or other shells.
 The instructions below are for go 1.7. or later.
 
-
 1. Download the Packer source (and its dependencies) by running
    `go get github.com/hashicorp/packer`. This will download the Packer source to
    `$GOPATH/src/github.com/hashicorp/packer`.
@@ -86,6 +85,24 @@ The instructions below are for go 1.7. or later.
 5. If everything works well and the tests pass, run `go fmt` on your code before
    submitting a pull-request.
 
+### Windows Systems
+On windows systems you need at least the [MinGW Tools](http://www.mingw.org/), e.g. install via [choco](https://chocolatey.org/):
+
+```
+choco install mingw -y
+```
+
+This installs the GCC compiler, as well as a ```mingw32-make``` which can be used wherever
+this documentation mentions ```make```
+
+when building using ```go``` you also need to mention the windows
+executable extension
+
+```
+go build -o bin/packer.exe
+```
+
+
 ### Opening an Pull Request
 
 Thank you for contributing! When you are ready to open a pull-request, you will