Docs: Add process for platform removal

Signed-off-by: Soby Mathew <soby.mathew@arm.com>
Change-Id: I3aefb16be610cb60270e8837bd8ce598c25a7f9a
diff --git a/docs/introduction/readme.rst b/docs/introduction/readme.rst
index d77e848..213af41 100644
--- a/docs/introduction/readme.rst
+++ b/docs/introduction/readme.rst
@@ -153,6 +153,9 @@
         - `PSoc64.
           <https://www.cypress.com/documentation/product-brochures/cypress-psoc-64-secure-microcontrollers>`_
 
+The document :doc:`Platform Deprecation and Removal </docs/contributing/platform_deprecation>`
+lists the deprecated platforms planned to be removed from upstream.
+
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