[1.8.x] Added link to section in docs/howto/custom-template-tags.txt.

~~~~~~~~~~~~~~~~~~~

Finally, register the tag with your module's ``Library`` instance, as explained

in "Writing custom template filters" above. Example::

in :ref:`writing custom template filters<howto-writing-custom-template-tags>`

above. Example::

    register.tag('current_time', do_current_time)