New section on external toolchain usage

docs/buildroot.html

@@ -36,6 +36,7 @@
       same buildroot source tree</a></li>
       <li><a href="#using_toolchain">Using the uClibc toolchain
       outside Buildroot</a></li>
+      <li><a href="#external_toolchain">Use an external toolchain</a></li>
       <li><a href="#downloaded_packages">Location of downloaded packages</a>
       </li>
       <li><a href="#add_software">Extending Buildroot with more
@@ -840,7 +841,43 @@ ln -s &lt;shared download location&gt; dl
 export BUILDROOT_DL_DIR &lt;shared download location&gt;
 </pre>
 
-
+    <h2><a name="external_toolchain" id="external_toolchain"></a>Using
+    an external toolchain</h2>
+
+<p>It might be useful not to use the toolchain generated by
+Buildroot, for example if you already have a toolchain that is known
+to work for your specific CPU, or if the toolchain generation feature
+of Buildroot is not sufficiently flexible for you (for example if you
+need to generate a system with <i>glibc</i> instead of
+<i>uClibc</i>). Buildroot supports using an <i>external
+toolchain</i>.</p>
+
+<p>To enable the use of an external toolchain, go in the
+<code>Toolchain</code> menu, and&nbsp;:</p>
+
+<ul>
+  <li>Select the <code>External binary toolchain</code> toolchain
+  type</li>
+  <li>Adjust the <code>External toolchain path</code>
+  appropriately. It should be set to a path where a bin/ directory
+  contains your cross-compiling tools</li>
+  <li>Adjust the <code>External toolchain prefix</code>, so that the
+  prefix, suffixed with <code>-gcc</code> or <code>-ld</code> will
+  correspond to your cross-compiling tools</li>
+</ul>
+
+<p>If you are using an external toolchain based on <i>uClibc</i>, the
+<code>Core C library from the external toolchain</code> and
+<code>Libraries to copy from the external toolchain</code> options
+should already have correct values. However, if your external
+toolchain is based on <i>glibc</i>, you'll have to change these values
+according to your cross-compiling toolchain.</p>
+
+<p>To generate external toolchains, we recommend using <a
+href="http://ymorin.is-a-geek.org/dokuwiki/projects/crosstool">Crosstool-NG</a>.
+It allows to generate toolchains based on <i>uClibc</i>, <i>glibc</i>
+and <i>eglibc</i> for a wide range of architectures, and has good
+community support.</p>
 
     <h2><a name="add_software" id="add_software"></a>Extending Buildroot with
     more software</h2>