ox-md.el (md): Export underlined text as verbatim

* ox-md.el (md): Export underlined text as verbatim.

Thanks to Rick Frankel for suggesting this.

lisp/ox-md.el

@@ -69,6 +69,7 @@ This variable can be set to either `atx' or `setext'."
 	       (org-open-file (org-md-export-to-markdown nil s v)))))))
   :translate-alist ((bold . org-md-bold)
 		    (code . org-md-verbatim)
+		    (underline . org-md-verbatim)
 		    (comment . (lambda (&rest args) ""))
 		    (comment-block . (lambda (&rest args) ""))
 		    (example-block . org-md-example-block)