Refactor top-level document structure

In preparation for extending documentation on PSA certified and
secure processing environments, the top-level structure has been
cleaned-up and simplified. PNGs from tf-m for docs home have
been reused for consistency.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Change-Id: Id2b7d9b46dd90f419d00c417a06003e32862ead0
diff --git a/docs/project/index.rst b/docs/project/index.rst
index 21f1d0f..d9bb409 100644
--- a/docs/project/index.rst
+++ b/docs/project/index.rst
@@ -1,4 +1,4 @@
-About the project
+About the Project
 =================
 
 .. toctree::
@@ -16,6 +16,6 @@
 
 --------------
 
-*Copyright (c) 2020-2021, Arm Limited and Contributors. All rights reserved.*
+*Copyright (c) 2020-2022, Arm Limited and Contributors. All rights reserved.*
 
 SPDX-License-Identifier: BSD-3-Clause