Install the package (a local editable installation is shown here) and emit your first record:
pip install .
from femtologging import FemtoStreamHandler, get_logger
logger = get_logger("demo.app")
logger.add_handler(FemtoStreamHandler.stderr())
logger.log("INFO", "hello from femtologging")
Handlers run in background threads, so remember to flush or close them before your process exits.