ref-manual: Typo found and fixed.

(From yocto-docs rev: 035c6bc2089b19b0d0ae332bca25a75211f86964)

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

documentation/ref-manual/ref-variables.xml

@@ -16833,7 +16833,7 @@
      USERADD_PACKAGES = "${PN}"
                     </literallayout>
                     <note>
-                        If follows that if you are going to use the
+                        It follows that if you are going to use the
                         <filename>USERADD_PACKAGES</filename> variable,
                         you need to set one or more of the
                         <link linkend='var-USERADD_PARAM'><filename>USERADD_PARAM</filename></link>,