Improvements in Readme

- Fix broken link to the issue tracker.
- Add contents section to make navigation easier throughout the page.
- Move the link to documentation contents near the top. Where it was
  before could be missed and documentation might seem inaccessible.

Change-Id: I502e4fc0fd312459cda351d30a8781c221625724
Signed-off-by: John Tsichritzis <john.tsichritzis@arm.com>

readme.rst

 Trusted Firmware-A - version 2.1
 ================================
 
+.. section-numbering::
+    :suffix: .
+
+.. contents::
+
 Trusted Firmware-A (TF-A) provides a reference implementation of secure world
 software for `Armv7-A and Armv8-A`_, including a `Secure Monitor`_ executing
 at Exception Level 3 (EL3). It implements various Arm interface standards,
@@ -27,6 +32,12 @@ 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.
 
+Documentation contents
+----------------------
+
+The `Trusted Firmware-A Documentation Contents`_ page contains an overview of
+the documentation that is available, with links to facilitate easier browsing.
+
 License
 -------
 
@@ -271,12 +282,6 @@ See the `Contributing Guidelines`_ for information on how to contribute to this
 project and the `Acknowledgments`_ file for a list of contributors to the
 project.
 
-Documentation contents
-~~~~~~~~~~~~~~~~~~~~~~
-
-The `Trusted Firmware-A Documentation Contents`_ page contains an overview of
-the documentation that is available, with links to facilitate easier browsing.
-
 IRC channel
 ~~~~~~~~~~~
 
@@ -328,7 +333,7 @@ Security advisories
 .. _NVIDIA Trusted Little Kernel: http://nv-tegra.nvidia.com/gitweb/?p=3rdparty/ote_partner/tlk.git;a=summary
 .. _Trusty Secure OS: https://source.android.com/security/trusty
 .. _trustedfirmware.org: https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git
-.. _issue tracker: http://issues.trustedfirmware.org
+.. _issue tracker: https://developer.trustedfirmware.org/project/board/1/
 .. _Security Center: ./docs/security-center.rst
 .. _license: ./license.rst
 .. _Contributing Guidelines: ./contributing.rst