example usage added

examples/README.md

examples/configuration/config.yaml

examples/federation_example.py

examples/integration_examples.py

examples/note_example.py

examples/run_example.py

requirements.txt

setup.py

src/pyfed/models/actors.py

src/pyfed/models/objects.py

src/pyfed/security/__init__.py

src/pyfed/security/http_signatures.py

src/pyfed/security/key_management.py

src/pyfed/security/validators.py

src/pyfed/serializers/json_serializer.py

src/pyfed/utils/exceptions.py

tests/unit_tests/models/__init__.py

tests/unit_tests/models/test_activities.py

tests/unit_tests/models/test_actors.py

tests/unit_tests/models/test_collections.py