docs: add docs for `Advanced Usage`, e.g modifying request/response

[WSH032]

Summary

Advanced Usage documentation

• examples about modifying requests/responses

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Close: #15

Checklist

• [x] I've read CONTRIBUTING.md.
• [x] I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• [x] I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• [x] I've updated the documentation accordingly.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (c7cec23) 96.74% compared to head (7fb9e95) 96.74%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #22 +/- ## ======================================= Coverage 96.74% 96.74% ======================================= Files 9 9 Lines 461 461 Branches 67 67 ======================================= Hits 446 446 Misses 9 9 Partials 6 6 ```

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