Create THIRD-PARTY-NOTICES.TXT

Create initial (empty) 3rd party notices with contact details

THIRD-PARTY-NOTICES.TXT

+.NET Core uses third-party libraries or other resources that may be
+distributed under licenses different than the .NET Core software.
+
+In the event that we accidentally failed to list a required notice, please
+bring it to our attention. Post an issue or email us:
+
+           dotnet@microsoft.com
+
+The attached notices are provided for information only.
+