doc: De-duplicate readme and license files

The readme.rst and license.rst files in the project root overlap
with the index.rst and license.rst files in the docs/ folder. We
need to use the latter when building the documentation, as Sphinx
requires all included files to be under a common root. However,
the files in the root are currently used by the cgit and Github
viewers.

Using symlinks in Git presents some difficulties so the best
course of action is likely to leave these files but in stub form.

The license.rst file in the root will simply tell the reader to
refer to docs/license.rst.

The readme.rst file will contain a small amount of content that
is derived from the docs/index.rst file, so that the Github main
page will have something valid to show, but it will also contain
a link to the full documentation on ReadTheDocs.

Change-Id: I6dc46f08777e8d7ecb32ca7afc07a28486c9f77a
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

docs/index.rst

@@ -43,10 +43,9 @@ states.
 Users are encouraged to do their own security validation, including penetration
 testing, on any secure world code derived from TF-A.
 
-Arm will continue development in collaboration with interested parties to
-provide a full reference implementation of Secure Monitor code and Arm standards
-to the benefit of all developers working with Armv7-A and Armv8-A TrustZone
-technology.
+In collaboration with interested parties, we will continue to enhance |TF-A|
+with reference implementations of Arm standards to benefit developers working
+with Armv7-A and Armv8-A TrustZone technology.
 
 Functionality
 -------------
@@ -133,8 +132,8 @@ Functionality
    The use of pointer authentication in the normal world is enabled whenever
    architectural support is available, without the need for additional build
    flags. Use of pointer authentication in the secure world remains an
-   experimental configuration at this time and requires the ``ENABLE_PAUTH``
-   build flag to be set.
+   experimental configuration at this time and requires the
+   ``BRANCH_PROTECTION`` option to be set to non-zero.
 
 -  Position-Independent Executable (PIE) support. Initially for BL31 only, with
    further support to be added in a future release.

license.rst

@@ -1,38 +1 @@
-Copyright (c) [XXXX-]YYYY, <OWNER>. All rights reserved.
-
-Redistribution and use in source and binary forms, with or without modification,
-are permitted provided that the following conditions are met:
-
--  Redistributions of source code must retain the above copyright notice, this
-   list of conditions and the following disclaimer.
-
--  Redistributions in binary form must reproduce the above copyright notice, this
-   list of conditions and the following disclaimer in the documentation and/or
-   other materials provided with the distribution.
-
--  Neither the name of Arm nor the names of its contributors may be used to
-   endorse or promote products derived from this software without specific prior
-   written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
-ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
-WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
-ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
-(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
-LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
-ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
-SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
---------------
-
-.. note::
-   Individual files contain the following tag instead of the full license text.
-
-::
-
-    SPDX-License-Identifier:    BSD-3-Clause
-
-This enables machine processing of license information based on the SPDX
-License Identifiers that are here available: http://spdx.org/licenses/
+See docs/license.rst