Fix a couple of typos reported by Detlef Lannert

<lannert@lannert.rz.uni-duesseldorf.de>.

Doc/doc/doc.tex

@@ -496,8 +496,8 @@ distribution, to create or maintain whole documents or sections.
     programming languages or even Python.
 
     \begin{macrodesc}{bifuncindex}{\p{name}}
-      Add a index entry referring to a built-in function named
-      \var{name}; parenthesis should not be included after
+      Add an index entry referring to a built-in function named
+      \var{name}; parentheses should not be included after
       \var{name}.
     \end{macrodesc}