UI Fix: Incomplete form to add todo object

In the first form in index.html, we allow the user to add a todo item to the list.
Steps to complete this form:
1. Add action and method attributes to below form.
2. Make a post request to the url 'add/' with the information provided by user.
3. Add csrf_token for security.
4. Add options 1, 2, 3 to the dropdown menu to set priority.