Docs: Restructure the documents

Restructure the file category to let it more friendly to users.

Signed-off-by: Summer Qin <summer.qin@arm.com>
Change-Id: I7ced0e2d700ce03423e472e0098608f3445ba169
diff --git a/platform/ext/index.rst b/platform/ext/index.rst
index d763c7c..1d12b9a 100644
--- a/platform/ext/index.rst
+++ b/platform/ext/index.rst
@@ -1,13 +1,13 @@
-Platforms
-=========
+Supported Platforms
+===================
 
 .. toctree::
     :maxdepth: 1
     :caption: Information
 
-    readme
     /platform/readme
-    /docs/contributing/platform_deprecation.rst
+    readme
+    /platform/ext/platform_deprecation.rst
 
 .. toctree::
     :maxdepth: 4
@@ -55,4 +55,4 @@
 
 --------------
 
-*Copyright (c) 2020, Arm Limited. All rights reserved.*
+*Copyright (c) 2020-2021, Arm Limited. All rights reserved.*