doc: unpack result to access TracerouteResult

[isidroas]

Fixes:

>>> a.world_trace()
AttributeError: 'tuple' object has no attribute 'world_trace'

Checklist:

• [X] If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• [ ] I squashed commits belonging together
• [ ] I added unit tests or explained why they are not relevant
• [ ] I executed the regression tests (using cd test && ./run_tests or tox)
• [ ] If the PR is still not finished, please create a Draft Pull Request