dev-manual: Fixed a grammar error

(From yocto-docs rev: 7b81f29a641cad4f10c3c721c0d40ce11d928648)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/dev-manual/dev-manual-model.xml

@@ -632,7 +632,7 @@
         </para>
 
         <para>
-            Three entry points exist that allow you develop using
+            Three entry points exist that allow you to develop using
             <filename>devtool</filename>:
             <itemizedlist>
                 <listitem><para><emphasis><filename>devtool add</filename></emphasis>