Add more detailed information on prerequisites for building naclports.

README.rst

 naclports - Ports of open source software to Native Client
 ==========================================================
 
 naclports is collection of open source libraries and applications that have
 been ported to Native Client, along with set to tools for building and
 maintaining them.
 
 The ports themselves live in the ``ports`` directory.  Each one contains of
 three main file:
 
 - pkg_info: a description of the package.
 - build.sh: a bash script for building it
 - nacl.patch: an optional patch file.
 
 The tools for building packages live in ``build_tools``.  To build and install
 a package into the toolchain run ``naclports.py install <package_dir>``.  This
 script will download, patch, build and install the application or library.  By
 default it will first build any dependencies that that the package has.
 
+Prerequistes
+------------
+
 The build scripts require that certain tools are present in the host system.
 You will need at least these:
 
 - bash
 - make
 - curl
 - sed
 - git
 
 To build all ports you will also need these:
 
 - cmake
 - texinfo
 - gettext
 - pkg-config
 - autoconf, automake, libtool
 - libglib2.0-dev >= 2.26.0 (if you want to build glib)
 
+On Mac OS X you can use homebrew to install these using the following command::
+
+  brew install autoconf automake cmake gettext libtool pkg-config
+
+To the build system for some of the native python modules relies on a 32-bit

[binji, 2014/04/17 17:43:33]

s/To the build/The build/

[Sam Clegg, 2014/04/17 17:48:42]

Done.

+host build of the python itself, which in turn relies on the development version

[binji, 2014/04/17 17:43:33]

s/the python/Python/

[Sam Clegg, 2014/04/17 17:48:42]

Done.

+of zlib being available.  On 64-bit Ubuntu/Precise this means installing the
+following package: ``lib32z1-dev``.

[binji, 2014/04/17 17:43:33]

What about on Mac OS X?

[Sam Clegg, 2014/04/17 17:48:42]

Not sure at this point :(

+
+
+Building
+--------
+
 Before you can build any of the package you must set the NACL_SDK_ROOT
 environment variable to top directory of a version of the Native Client SDK
 (the directory containing toolchain/). This path should be absolute.
 
 The top level Makefile can be used as a quick way to build one or more
 packages. For example, ``make vorbis`` will build ``libvorbis-1.2.3`` and
 ``libogg-1.1.4``. ``make all`` will build all the packages.
 
 There are 4 possible architectures that NaCl modules can be compiled for: i686,
 x86_64, arm, pnacl. The naclports build system will only build just one at at
@@ skipping 119 matching lines @@
 
 1. Directly modify the sources in ``out/build/PKG_NAME``.
 2. Build the package and verify the changes.
 3. Use ``git diff upstream.. > ../path/to/nacl.patch`` to regenerate
    the patch file.
 
 Whenever the upstream archive or patch file changes and you try to build the
 package you will be prompted to remove the existing repository and start a new
 one. This is to avoid deleting a repository that might have unsaved changed.
 
-
 Happy porting!