docs: add links to other pages

Author: kenjis

user_guide_src/source/installation/upgrade_views.rst

@@ -16,8 +16,9 @@ What has been changed
 
 - Your views look much like before, but they are invoked differently ... instead of CI3's
   ``$this->load->view('x');``, you can use ``return view('x');``.
-- CI4 supports *View Cells* to build your response in pieces, and *View Layouts* for page layout.
-- The template parser is still there, and substantially enhanced.
+- CI4 supports :doc:`../outgoing/view_cells` to build your response in pieces,
+  and :doc:`../outgoing/view_layouts` for page layout.
+- The :doc:`Template Parser <../outgoing/view_parser>` is still there, and substantially enhanced.
 
 Upgrade Guide
 =============