Platform/Sgi: add platform documentation

Add a document that provides information about the platforms supported
by the package 'SgiPkg', the build environment, links to additional
documentation and corresponding platform fvp.

Signed-off-by: Thomas Abraham <[email protected]>
Reviewed-by: Sami Mujawar <[email protected]>

Author: Thomas Abraham

Platform/ARM/SgiPkg/Readme.md

@@ -0,0 +1,35 @@
+Arm Neoverse Reference Design Platforms
+=======================================
+
+# Introduction
+
+This document lists information related to the usage of EDKII firmware for Arm's
+Neoverse Reference Design platforms. Details about Arm's Neoverse Reference
+Design platforms is listed on this [page](https://gitlab.arm.com/arm-reference-solutions/arm-reference-solutions-docs/-/tree/master/docs/infra)
+
+The platform code is located under Platform/Arm/SgiPkg. Following platforms are
+supported in this platform code.
+
+- [RD-N2](https://gitlab.arm.com/arm-reference-solutions/arm-reference-solutions-docs/-/tree/master/docs/infra/rdn2)
+- [RD-V1](https://gitlab.arm.com/arm-reference-solutions/arm-reference-solutions-docs/-/tree/master/docs/infra/rdv1)
+- [RD-V1-MC](https://gitlab.arm.com/arm-reference-solutions/arm-reference-solutions-docs/-/tree/master/docs/infra/rdv1mc)
+- [RD-N1-Edge](https://gitlab.arm.com/arm-reference-solutions/arm-reference-solutions-docs/-/tree/master/docs/infra/rdn1edge)
+- [RD-N1-Edge-X2](https://gitlab.arm.com/arm-reference-solutions/arm-reference-solutions-docs/-/tree/master/docs/infra/rdn1edgex2)
+- [RD-E1-Edge](https://gitlab.arm.com/arm-reference-solutions/arm-reference-solutions-docs/-/tree/master/docs/infra/rde1edge)
+- [SGI-575](https://gitlab.arm.com/arm-reference-solutions/arm-reference-solutions-docs/-/tree/master/docs/infra/sgi575)
+
+# Build Environment
+
+- x86 Linux host machines running Ubuntu 18.04 or later
+- [Toolchain](https://developer.arm.com/-/media/Files/downloads/gnu-a/8.3-2019.03/binrel/gcc-arm-8.3-2019.03-x86_64-aarch64-linux-gnu.tar.xz)
+
+# How to build and execute
+
+Please follow top-level Readme.md for build instructions. For details on building
+the rest of the software components and executing it using the platform FVP, use
+the links to the respective platforms listed above.
+
+# Obtaining the platform fvp
+
+The fixed virtual platform for the supported platforms can be obtained
+[here](https://developer.arm.com/tools-and-software/open-source-software/arm-platforms-software/arm-ecosystem-fvps)