added windows installation section in the Installation.md

Signed-off-by: gisphm <phmfk@hotmail.com>

Installation.md

@@ -26,3 +26,23 @@ One-liner:
 ```bash
 curl -sSL http://git.io/git-extras-setup | sudo bash /dev/stdin
 ```
+
+## Windows (use it at your own risk)
+
+First, please install `Git for Windows 2.x` from 'https://github.com/git-for-windows/git/releases'
+and the basic [msys2][1].
+Second, clone the `git-extras` repo into any folder you like.
+```bash
+git clone https://github.com/tj/git-extras.git
+```
+After that, open the script `install.cmd` in the folder with any text editor you like.
+Modify the `PREFIX` variable to where your `Git for Windows 2.x` is installed.
+For example, I install it in the folder called `C:\SCM\PortableGit` and
+the `PREFIX` should be `C:\SCM\PortableGit\mingw64` (for 64-bit release)
+or `C:\SCM\PortableGit\mingw32` (for 32-bit release).
+Third, execute the `install.cmd` directly or in the command prompt.
+Last, please copy `colrm.exe` and `column.exe` from `folder-your-msys2-installed/usr/bin` to
+`folder-your-git-installed/usr/bin`.
+Enjoy `git-extras`!
+
+[1]: http://sourceforge.net/projects/msys2/