ref-manual: Added USE_VT variable description.

(From yocto-docs rev: c56cea783f87932de7ba6c02a1256f1303298f48)

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

documentation/ref-manual/ref-variables.xml

@@ -9487,6 +9487,28 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
             </glossdef>
         </glossentry>
 
+        <glossentry id='var-USE_VT'><glossterm>USE_VT</glossterm>
+            <glossdef>
+                <para>
+                    When using
+                    <ulink url='&YOCTO_DOCS_DEV_URL;#new-recipe-enabling-system-services'>SysVinit</ulink>,
+                    determines whether or not to run a
+                    <ulink url='http://en.wikipedia.org/wiki/Getty_%28Unix%29'>getty</ulink>
+                    on any virtual terminals in order to enable logging in
+                    through those terminals.
+                </para>
+
+                <para>
+                    The default value used for <filename>USE_VT</filename>
+                    is "1" when no default value is specifically set.
+                    Typically, you would set <filename>USE_VT</filename>
+                    to "0" in the machine configuration file for machines
+                    that do not have a graphical display attached and
+                    therefore do not need virtual terminal functionality.
+                </para>
+            </glossdef>
+        </glossentry>
+
         <glossentry id='var-USER_CLASSES'><glossterm>USER_CLASSES</glossterm>
             <glossdef>
                 <para>