Update html.parser.rst (GH-30678)

Update html.parser.rst (GH-30678)

This PR for the documentation of the [html.parser](https://docs.python.org/3/library/html.parser.html) module will

- fix a terminology mistake (‘start of a tag’ -> ‘start tag of an element’);
- mention the parameter names of the `HTMLParser.handle_*` methods where missing.