More text on the accept invitation page.
Add a message to a newly invited user after setting their password.
Add link to share instance on home and add speech pages.

The templates in the sayit app don't have very many blocks at the moment,
which makes them rather hard to extend. The best I can see to do to for
adding this link is to put it at the top of the content block.

django-apptemplates allows us to extend the templates from speeches
without having to give them new names.
Add a new speech button to instance home page.

Also add a new section button and style the get help link as a button.
Placate flake8.