documentation/bsp-guide/bsp.xml: Updated Example Filesystem Layout

Added more explanation about the base directory (meta-<bsp_name>) to the
Example Filesystem Layout section.  These changes were suggested by
Tom Zanussi to help users understand better how to add BSP layers
to the build system.

(From yocto-docs rev: 66b05e2b3096539b746f1b597ea8f542bba6be3f)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/bsp-guide/bsp.xml

@@ -60,6 +60,9 @@
                 <literallayout class='monospaced'>
      meta-&lt;bsp_name&gt;
                 </literallayout>
+            </para>
+
+            <para>
                 "bsp_name" is a placeholder for the machine or platform name.
                 Here are some example base directory names:
                 <literallayout class='monospaced'>
@@ -69,6 +72,23 @@
                 </literallayout>
             </para>
 
+            <para>
+                The base directory (<filename>meta-&lt;bsp_name&gt;</filename>) is the root of the BSP layer.
+                This root is what you add to the BBLAYERS variable in <filename>build/conf/bblayers.conf</filename>
+                so that the build system recognizes the BSP definition and from it can build an image.
+                Here is an example:
+                <literallayout class='monospaced'>
+     BBLAYERS = " \
+        /usr/local/src/yocto/meta \
+        /usr/local/src/yocto/meta-yocto \
+        /usr/local/src/yocto/meta-&lt;bsp_name&gt; \
+        "
+                </literallayout>
+                For more detailed information on layers, see the 
+                <ulink url='http://www.yoctoproject.org/docs/poky-ref-manual/poky-ref-manual.html#usingpoky-changes-layers'>
+                BitBake Layers</ulink> section of the Poky Reference Manual.
+            </para>
+
             <para>
                 Below is the common form for the file structure inside a base directory.
                 While you can use this basic form for the standard, realize that the actual structures