docs/select: Add an article.

docs/library/select.rst

@@ -61,7 +61,7 @@ Methods
    list of (``obj``, ``event``, ...) tuples, ``event`` element specifies
    which events happened with a stream and is a combination of `select.POLL*`
    constants described above. There may be other elements in tuple, depending
-   on platform and version, so don't assume that its size is 2. In case of
+   on a platform and version, so don't assume that its size is 2. In case of
    timeout, an empty list is returned.
 
    Timeout is in milliseconds.