message: Update README.md with prerequisite of Targeting Pack
  <!-- Please review the items on the PR checklist before submitting-->
  ## PR Checklist
  * [x] Closes
  * [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
diff: @@ -299,6 +299,7 @@ If you would like to ask a question that you feel doesn't warrant an issue
  * Universal Windows Platform Development
  * **The following Individual Components**
  * C++ (v142) Universal Windows Platform Tools
  +* You must install the [.NET Framework Targeting Pack](https://docs.microsoft.com/dotnet/framework/install/guide-for-developers#to-install-the-net-framework-developer-pack-or-targeting-pack) to build test projects
  ## Building the Code
  