Add support for documentation build as a target in Makefile

Command to build HTML-formatted pages from docs:
make doc

Change-Id: I4103c804b3564fe67d8fc5a3373679daabf3f2e9
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
diff --git a/docs/getting_started/docs-build.rst b/docs/getting_started/docs-build.rst
index c5625e9..91b1b3a 100644
--- a/docs/getting_started/docs-build.rst
+++ b/docs/getting_started/docs-build.rst
@@ -56,21 +56,28 @@
 Building rendered documentation
 -------------------------------
 
-From the ``docs`` directory of the project, run the following commands. It is
-important to note that you will not get the correct result if the commands are
-run from the project root directory, as that would invoke the top-level Makefile
-for |TF-A| itself.
+Documents can be built into HTML-formatted pages from project root directory by
+running the following command.
 
 .. code:: shell
 
-   make clean
-   make html
+   make doc
 
 Output from the build process will be placed in:
 
 ::
 
-   <tf-a root>/docs/build/html/
+   docs/build/html/
+
+We also support building documentation in other formats. From the ``docs``
+directory of the project, run the following command to see the supported
+formats. It is important to note that you will not get the correct result if
+the command is run from the project root directory, as that would invoke the
+top-level Makefile for |TF-A| itself.
+
+.. code:: shell
+
+   make help
 
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