infra: add a top level introduction for neoverse platforms

Add a introduction page as a starting point for all the neoverse
platform software stack. List all the platforms supported on this
page with corresponding links to the platform software.
Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: I524b3a26c63af50a605e72a518badd4b5102c691

docs/infra/readme.rst

+Neoverse Reference Design Platform Software
+===========================================
+
+Neoverse reference designs provide useful resources with best practices on how
+to integrate a Neoverse compute subsystem within a larger SoC. These compute
+subsystems are targeted at addressing requirements for specific applications in
+the cloud-to-edge infrastructure markets.
+
+The Neoverse reference designs are also available as fixed virtual platform
+models and provides a platform to explore various aspects of the compute
+subsystem design from a software perspective. A software stack is also made
+available as part of the Neoverse reference designs.
+
+The platform software stack that can be used along with the fixed virtual
+platforms is available for the following reference design platforms.
+
+1. `RD-N2`_
+2. `RD-V1 (single chip)`_
+3. `RD-V1 (quad chip)`_
+4. `RD-N1-Edge (single chip)`_
+5. `RD-N1-Edge (dual chip)`_
+6. `RD-E1-Edge`_
+7. `SGI-575`_  (former system guidance platform)
+
+The links above provide detailed documentation about the platform documentation
+and includes instructions on downloading the software stack, compiling it,
+executing the software stack on a fixed virtual platform and information about
+the various features supported by the software stack.
+
+For questions about the Neoverse Reference Design platform software stack, write
+to support-subsystem-enterprise@arm.com.
+
+--------------
+
+*Copyright (c) 2021, Arm Limited. All rights reserved.*
+
+
+.. _RD-N2: docs/infra/rdn2
+.. _RD-V1 (single chip): docs/infra/rdv1
+.. _RD-V1 (quad chip): docs/infra/rdv1mc
+.. _RD-N1-Edge (single chip): docs/infra/rdn1edge
+.. _RD-N1-Edge (dual chip): docs/infra/rdn1edgex2
+.. _RD-E1-Edge: docs/infra/rde1edge
+.. _SGI-575: docs/infra/sgi575