Add note to indicate deprecation of MS ANGLE repo

Temporary workaround for #2860 until @vnen gets around to writing a more fleshed out build instruction.

development/compiling/compiling_for_uwp.rst

@@ -17,6 +17,15 @@ Requirements
    ``ms_master`` (default) branch. Keep it in a path without spaces to
    avoid problems.
 
+.. note:: The ANGLE repo by Microsoft has been discontinued and the
+          ``ms_master`` branch has been cleared out.
+          
+          As a temporary workaround however, it is still possible to
+          download an older state of the source code via commit `c61d048 <https://github.com/microsoft/angle/tree/c61d0488abd9663e0d4d2450db7345baa2c0dfb6>`__.
+          
+          This page will eventually be updated in the future to reflect
+          the new build instructions.
+
 .. seealso:: For a general overview of SCons usage for Godot, see
              :ref:`doc_introduction_to_the_buildsystem`.