docs: ADK2 docs - update alternative build instructions

<h3 id="alt-build">Using the ADK Alternative Build System</h3>

<p>An alternative build and load system is also available for the ADK 2012. This system is command

line based and intended for production environments where using an IDE environment to load software

onto accessory hardware may be inconvenient or undesirable.</p>

<p>An alternative, make file-based build and upload system is also available for the ADK 2012. This

system is command line based and intended for production environments where using an IDE environment

to load software onto accessory hardware may be inconvenient or undesirable.</p>

<p>To use the command line based build system:</p>

<p>To setup the environment:</p>

<ol>

  <li><a href="#src-download">Download</a> the ADK 2012 source code files.</li>

  <li>Download and install the <a href="http://www.gnu.org/software/make/">make</a> tool on your

development system.</li>

  <li>Update your system’s PATH to include {@code

&lt;adk-source-download&gt;/external/toolchain/bin}.</li>

  <li>Open a terminal window, navigate to {@code

<adk-source-download>/external/toolchain/app} and execute the following command:

  <pre>$> make</pre></li>

  <li>In a terminal window, navigate to {@code

&lt;adk-source-download&gt;/adk2012/board/MakefileBasedBuild}.</li>

  <li>Execute the following command and follow the instructions:

    <pre>$> ./setup</pre>

  </li>

</ol>

<p>To build a program for your accessory:</p>

<ol>

  <li>Place your accessory code in the {@code MakefileBasedBuild/app} directory, including all

required library files. See the {@code app/main.c} file for an example of the program format.</li>

  <li>Execute the following command and follow the instructions:

    <pre>$> ./build</pre>

  </li>

</ol>

<p>To load the program on your accessory hardware:</p>

<ol>

  <li>Run the build process above and make sure your program compiled successfully.</li>

  <li>Attach the accessory via USB cable to your development computer.</li>

  <li>Check which port the accessory is attached to and modify the {@code UART} variable in the

{@code flash} script to the correct port address. On linux machines, the port address is typically

{@code /dev/ttyUSB0}.</li>

  <li>Execute the following command to load the program on the accessory:

  <pre>$> ./flash</pre></li>

</ol>

<h2 id="adk-conn">How the ADK Connects with Android Devices</h2>