Capitalize first letter of an explanation for a \versionchanged

annotation.

Doc/lib/libos.tex

@@ -785,7 +785,7 @@ If \var{times} is \code{None}, then the file's access and modified
 times are set to the current time.  Otherwise, \var{times} must be a
 2-tuple of numbers, of the form \code{(\var{atime}, \var{mtime})}
 which is used to set the access and modified times, respectively.
-\versionchanged[added support for \code{None} for \var{times}]{2.0}
+\versionchanged[Added support for \code{None} for \var{times}]{2.0}
 Availability: Macintosh, \UNIX{}, Windows.
 \end{funcdesc}