added a few more notes to documentation

Note, the exposer of port 3306 is probably a mistake. The PostgrSQL default port is 5432 which is also used in `./tornado-backend/blog.py` to connect to the database.

Note also, the python image used installs tornado version 6.2, thus the `set_secure_cookie` and `get_secure_cookie` instead of `set_signed_cookie` and `get_signed_cookie` used in `./tornado-backend/blog.py`. The naming of these methods changed with tornado version 6.3. This is another mistake in the blog demo on GitHub. ([see](https://www.tornadoweb.org/en/stable/web.html#))

### Visualization

```mermaid

Note, Tornado is used as web server and web framework e.g. with frontend and backend

### More Details

* More details on the general architecture of a tornado web app can be found [here](https://www.tornadoweb.org/en/stable/guide/structure.html)

* 

## Launch Web App

### Step 1) Change to `tornado-backend` directory