Document that filter is added in 2.2.

Doc/lib/libfnmatch.tex

@@ -47,6 +47,7 @@ false; the comparison is case-sensitive.
 Return the subset of the list of \var{names} that match \var{pattern}.
 It is the same as \code{[n for n in names if fnmatch(n, pattern)]}, but
 implemented more efficiently.
+\versionadded{2.2}
 \end{funcdesc}
 
 \begin{seealso}