infra/sgi575: add user guide for sgi-575 platform

Add the initial user guide for the SGI-575 platform software stack. The
user guide points to documents that provide information about obtaining
the platform software stack and using the various features it supports.
A table to list the release tags is included as well.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: I4730ee89ece766577708126cec3cf0bc9e878bc3

docs/infra/sgi575/readme.rst

+SGI-575 platform software user guide
+====================================
+
+.. contents::
+
+
+Introduction
+------------
+
+SGI (System Guidance for Infrastructure) is a collection of resources to provide
+a representative view of typical compute subsystems that can be designed and
+implemented using specific generations of Arm IP. SGI-575 in particular is based
+on the following hardware configuration.
+
+- 8x Cortex-A75 with private L2 Cache
+- DynamIQ with L3 Cache options
+- System Level Cache options
+- Up to 2x DDR4-3200 (DMC-620)
+- Arm Cortex-M7 for System Control Processor (SCP) and
+  Manageability Control Processor (MCP)
+
+This document is a user guide on how to setup, build and run the SGI-575
+software stack on the Fixed Virtual Platform.
+
+
+Setting up the Host Machine and downloading the software stack
+--------------------------------------------------------------
+
+Host Machine requirements and the necessary steps to be followed to sync the
+software stack are listed on '`Download sources`_' page.
+
+
+Obtaining the SGI-575 Fast Model
+--------------------------------
+
+The latest version of SGI-575 Fast Model can be requested by sending a email
+to Arm at this email address: `support-connect@arm.com <mailto:support-connect@arm.com>`_.
+
+Follow the instruction in the installer and setup the FVP. Typically, the
+installer will ask to create a new folder in the home directory. You can either
+install the FVP in the home folder, or in the ``fastmodel/refinfra`` folder
+inside the workspace. If you would like to install in the ``fastmodel/refinfra``
+folder, when asked for the install location, provide the absolute path of the
+``fastmodel/refinfra``.
+
+
+Supported features
+------------------
+
+SGI-575 platform software stack supports the following features.
+
+- `Busybox Boot`_
+- `Buildroot Boot`_
+- `Linux Distribution Boot`_
+- `UEFI Secure Boot`_
+- `DMC-620 RAS`_
+
+Follow the links above for detailed information about the build and execute
+steps for each of the supported features.
+
+
+Release Tags
+------------
+
+Table below lists the release tags for the SGI-575 platform software stack and
+the corresponding SGI-575 FVP version that is recommended to be used along
+with the listed release tag. The summary of the changes introduced and tests
+validated in each release is listed in `change log`_.
+
++-----------------------+------------------------+
+|     Release Tag       |   SGI-575 FVP Version  |
++=======================+========================+
+|  RD-INFRA-2021.02.24  |       11.13.43         |
++-----------------------+------------------------+
+
+
+--------------
+
+*Copyright (c) 2021, Arm Limited. All rights reserved.*
+
+
+.. _Busybox Boot: docs/infra/common/busybox-boot.rst
+.. _Buildroot Boot: docs/infra/common/buildroot-boot.rst
+.. _Linux Distribution Boot: docs/infra/common/distro-boot.rst
+.. _UEFI Secure Boot: docs/infra/common/secure-boot.rst
+.. _DMC-620 RAS: docs/infra/common/dmc620-ras.rst
+.. _Download sources: docs/infra/common/download-sources.rst
+.. _change log: docs/infra/change-log.rst