Fix a minor markup typo.

Doc/doc/doc.tex

@@ -1598,7 +1598,7 @@ This \UNIX\ is also followed by a space.
         but GNU \program{make} is required for the experimental
         processes in \file{Doc/tools/sgmlconv/}, at least while
         they're experimental.  This is not required for running the
-        \rpgram{mkhowto} script.
+        \program{mkhowto} script.
 
       \item[\program{makeindex}]
         This is a standard program for converting \LaTeX{} index data