ref-manual: Review comments applied for patch session

Paul Eggleton provided quite a series of patches that I previously
applied.  These changes represent the edits from an interactive
review he conducted with me.  The series of changes represents
his review for the entire set of changes in the original patch
series.

(From yocto-docs rev: e26f615a01de2b101e97eb6fd7175b813f74295e)

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

documentation/ref-manual/ref-classes.xml

@@ -632,7 +632,7 @@
         To exclude some recipes from having their work directories deleted by
         <filename>rm_work</filename>, you can add the names of the recipe or 
         recipes you are working on to the <filename>RM_WORK_EXCLUDE</filename> 
-        variable, which is also found in your <filename>local.conf</filename>
+        variable, which can also be set in your <filename>local.conf</filename>
         file.
         Here is an example:
         <literallayout class='monospaced'>