Update windows-requirements.md (dotnet#90)

Author: eiriktsarpalis

docs/building/windows-requirements.md

@@ -10,7 +10,12 @@ You must install several components to build the dotnet/runtime repository. Thes
 
 ## Enable Long Paths
 
-The runtime repository requires long paths to be enabled. Follow the instructions provided here to modify the registry to opt into that feature: https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#enable-long-paths-in-windows-10-version-1607-and-later
+The runtime repository requires long paths to be enabled. Follow the instructions provided here to modify the registry to opt into that feature: https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file#enable-long-paths-in-windows-10-version-1607-and-later. 
+
+If using msysgit (aka Git for Windows) you might need to also configure long paths there. Using an admin terminal simply type:
+```powershell
+PS> git config --system core.longpaths true
+```
 
 ## Visual Studio