[iostream.forward.overview] Convert incomplete wording with no normative

effect to an example.

Author: zygoloid

source/iostreams.tex

@@ -366,8 +366,7 @@
 \tcode{fpos}
 are
 used for specifying file position information.
-
-\pnum
+\begin{example}
 The types
 \tcode{streampos}
 and
@@ -377,6 +376,7 @@
 and
 \tcode{wchar_t}
 respectively.
+\end{example}
 
 \pnum
 \begin{note}