Fix typo reported by Paul Clifford.
Note that there is no str.joinfields(), use str.join() instead.
diff --git a/Doc/lib/libstring.tex b/Doc/lib/libstring.tex
index 897e5ea..99bb5ee 100644
--- a/Doc/lib/libstring.tex
+++ b/Doc/lib/libstring.tex
@@ -230,9 +230,11 @@
 \end{funcdesc}
 
 \begin{funcdesc}{joinfields}{words\optional{, sep}}
-  This function behaves identical to \function{join()}.  (In the past, 
+  This function behaves identically to \function{join()}.  (In the past, 
   \function{join()} was only used with one argument, while
   \function{joinfields()} was only used with two arguments.)
+  Note that there is no \method{joinfields()} method on string
+  objects; use the \method{join()} method instead.
 \end{funcdesc}
 
 \begin{funcdesc}{lstrip}{s\optional{, chars}}