Update Unix contrib document

The Ubuntu image with enhanced mode support is now built into the
Hyper-V create experience. Update the documentation to reflect that
instead of pointing to the old manual way.

docs/contributing/Building, Debugging, and Testing on Unix.md

@@ -79,23 +79,19 @@ Note: this variables can also be used on Windows as well.
 ## Ubuntu 18.04
 The recommended OS for developing Roslyn is Ubuntu 18.04. This guide was written using Ubuntu 18.04 but should be 
 applicable to most Linux enviroments. Ubuntu 18.04 was chosen here due to it's support for enhanced VMs in Hyper-V. 
-This makes it easier to use from a Windows machine.
+This makes it easier to use from a Windows machine: full screen, copy / paste, etc ...
 
 ### Hyper-V
-When using Hyper-V to develop you will want to enable enhanced mode. This allows for the VM to be full screen, have 
-clipboard access and support additional devices. Ubuntu 18.04 is the first Linux OS supported in this mode. The 
-mileage with other distros may vary.
+Hyper-V has a builtin Ubuntu 18.04 image which supports enhanced mode. Here is a tutorial for creating 
+such an image:
 
-Enhanced mode support is still fairly new and does require a few manual steps. They are all covered in this 
-blog post:
+https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/quick-start/quick-create-virtual-machine
 
-https://blogs.technet.microsoft.com/virtualization/2018/02/28/sneak-peek-taking-a-spin-with-enhanced-linux-vms/
+When following this make sure to:
+1. Click Installation Source and uncheck "Windows Secure Boot"
+1. Complete the Ubuntu installation wizard. Full screen mode won't be available until this is done.
 
-Following the steps on that blog post will get you to a point where you can the features you are looking for. There are
- a couple of deviations from the instructions there:
-
-- There is no longer a config-user.sh script
-- cd into `ubuntu/18.04` instead of `ubuntu/16.04`
+Overall this takes about 5-10 minutes to complete. 
 
 ### Source Link
 Many of the repositories that need to be built use source link and it crashes on Ubuntu 18.04 due to dependency changes.