Add building instructions for Mac OS X

docs/development/Building in Mac OS X.md

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+# Building in Mac OS X
+
+Building in Mac OS X can be accomplished in just a few steps:
+
+* Install general development tools (clang, make, git)
+* Install ARM GCC 4.8 series compiler
+* Checkout Cleanflight sourcecode through git
+* Build the code
+
+## Install general development tools (clang, make, git)
+
+Open up a terminal and run `make`. If it is installed already, you should see a message like this, which means that you
+already have the required development tools installed:
+
+```
+make: *** No targets specified and no makefile found.  Stop.
+```
+
+If it isn't installed yet, you might get a popup like this. If so, click the "install" button to install the commandline
+developer tools:
+
+![Prompt to install developer tools](assets/mac-prompt-tools-install.png)
+
+If you just get an error like this instead of a helpful popup prompt:
+
+```
+-bash: make: command not found
+```
+
+Try running `xcode-select --install` instead to trigger the popup.
+
+If that doesn't work, you'll need to install the XCode development environment [from the App Store][]. After
+installation, open up XCode and enter its preferences menu. Go to the "downloads" tab and install the 
+"command line tools" package.
+
+[from the App Store]: https://itunes.apple.com/us/app/xcode/id497799835
+
+## Install ARM GCC 4.8 series compiler
+
+Cleanflight is built using the 4.8 series GCC compiler provided by the [GNU Tools for ARM Embedded Processors project][].
+The newest "4.9" series compiler produces builds that don't boot on CC3D and Sparky targets (and perhaps others), so it's
+better to use the older 4.8 compiler for the moment.
+
+Hit the "all downloads" link on the right side of the GNU Tools for ARM page to view [the older releases][]. Grab the
+Mac installation tarball for the latest version in the 4.8 series (e.g. 4.8-2014-q3-update). Move it somewhere useful 
+such as a `~/development` folder (in your home directory) and double click it to unpack it. You should end up with a 
+folder called `~/development/gcc-arm-none-eabi-4_8-2014q3/`.
+
+Now you just need to add the `bin/` directory from inside the GCC directory to your system's path. Run `nano ~/.profile`. Add a
+new line at the end of the file which adds the path for the `bin/` folder to your path, like so:
+
+```
+export PATH=$PATH:~/development/gcc-arm-none-eabi-4_8-2014q3/bin
+```
+
+Press CTRL+X to exit nano, and answer "y" when prompted to save your changes.
+
+Now *close this terminal window* and open a new one. Try running:
+
+```
+arm-none-eabi-gcc --version
+```
+
+You should get output similar to:
+
+```
+arm-none-eabi-gcc (GNU Tools for ARM Embedded Processors) 4.8.4 20140725 (release) [ARM/embedded-4_8-branch revision 213147]
+Copyright (C) 2013 Free Software Foundation, Inc.
+This is free software; see the source for copying conditions.  There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+```
+
+If `arm-none-eabi-gcc` couldn't be found, go back and check that you entered the correct path in your `~/.profile` file.
+
+[GNU Tools for ARM Embedded Processors project]: https://launchpad.net/gcc-arm-embedded
+[the older releases]: https://launchpad.net/gcc-arm-embedded/+download
+
+## Checkout CleanFlight sourcecode through git
+
+Enter your development directory and clone the [Cleanflight repository][] using the "HTTPS clone URL" which is shown on
+the right side of the Cleanflight GitHub page, like so:
+
+```
+git clone https://github.com/cleanflight/cleanflight.git
+```
+
+This will download the entire Cleanflight repository for you into a new folder called "cleanflight".
+
+[CleanFlight repository]: https://github.com/cleanflight/cleanflight
+
+## Build the code
+
+Enter the cleanflight directory and run `make TARGET=NAZE` to build firmware for the Naze32. When the build completes,
+the .hex firmware should be available as `obj/cleanflight_NAZE.hex` for you to flash using the Cleanflight
+Configurator.
+
+## Updating to the latest source
+
+If you want to erase your local changes and update to the latest version of the Cleanflight source, enter your
+cleanflight directory and run these commands to first erase your local changes, fetch and merge the latest
+changes from the repository, then rebuild the firmware:
+
+```
+git reset --hard
+git pull
+
+make clean TARGET=NAZE
+make TARGET=NAZE
+```