[Cookbook][Configuration] tweaks for the web server configuration chapter

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed tickets | 

Tweaks to #3915 as suggested by @weaverryan.
```rst
The ``web/`` directory will be the document root...
```

```rst
... this directory is ``/var/www/project/web/``.
```