Clarify Fragment construtor javadoc.

     * arguments can be supplied by the caller with {@link #setArguments}

     * and later retrieved by the Fragment with {@link #getArguments}.

     *

     * <p>Applications should generally not implement a constructor.  The

     * first place application code can run where the fragment is ready to

     * be used is in {@link #onAttach(Activity)}, the point where the fragment

     * is actually associated with its activity.  Some applications may also

     * want to implement {@link #onInflate} to retrieve attributes from a

     * layout resource, though should take care here because this happens for

     * the fragment is attached to its activity.

     * <p>Applications should generally not implement a constructor. Prefer

     * {@link #onAttach(Context)} instead. It is the first place application code can run where

     * the fragment is ready to be used - the point where the fragment is actually associated with

     * its context. Some applications may also want to implement {@link #onInflate} to retrieve

     * attributes from a layout resource, although note this happens when the fragment is attached.

     */

    public Fragment() {

    }