add some documentation about buildroot's patch system

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+
+<h2>Buildroot patch structure</h2>
+
+<p>
+<h4>Keeping track of applied patches</h4>
+Whenever a patch is applied to a source code directory in buildroot, a text file named .applied_patches_list is created inside that source directory. 
+This file contains a list of all the patch filenames that were applied to that source code, just for reference. 
+</p>
+
+<p>
+<h4>Linux kernel patches</h4>
+The Linux kernel has several patch levels available for it in the buildroot patch system. 
+Buildroot first downloads the chosen kernel source from the mirror site, followed by any selected minor patch.
+Buildroot then extracts the kernel source from the compressed file and applies the minor patch, if one was chosen.
+After extracting the source and applying the official minor patch, buildroot looks for more patches in the following locations and in the order shown:
+
+<ol>
+<li> a custom, user downloaded kernel patch can be located in $(DL_DIR) and the filename is stored as $(LINUX26_BSP_PATCH) </li>
+<li> Atmel keeps their official kernel patches in target/device/Atmel/Linux/kernel-patches with subdirectories for each kernel release. 
+They also keep any board-specific patches in $(BR2_BOARD_PATH) </li>
+<li> globally available patches are kept in toolchain/kernel-headers </li>
+<li> IPMI (<a href="http://www.intel.com/design/servers/ipmi/ipmi.htm">Intelligent Platform Management Interface</a>) 
+kernel patches are kept in toolchain/kernel-headers/ipmi </li>
+<li> LZMA kernel compression support patches are kept in toolchain/kernel-headers/lzma </li>
+<li> <a href="http://www.realtimelinuxfoundation.org/downloads/downloads.html">Real-time Linux kernel</a> patches are kept in $(LINUX_RT_SOURCE) </li>
+<li> <a href="http://www.openswan.org/">Openswan</a> kernel patches are kept in package/openswan </li>
+</ol>
+</p>
+ 
+ <p>
+ <h4>Package source patches</h4>
+ Any patches for the Linux programs supported by buildroot are kept in that program's corresponding package/ directory.
+ </p>
+ 
+ <p>
+ <h4>How the patching is done</h4>
+Patches are applied in buildroot by running a shell script called toolchain/patch-kernel.sh with three arguments. The first argument is the target directory
+where the source code to be patched is saved. The second argument is the directory where the patch is saved. The third argument is the filename pattern
+to match when looking in the patch directory. The third argument can include wildcards to select multiple patch files. 
+</p>
+
+<!--#include file="footer.html" -->