Initial release

This release includes an antenna data recording I made in November 2023 with my RTL-SDR, connected to a patch antenna sensitive to 1.57542MHz and tuned to this frequency. The recording was taken in St. Ives, Cambridgeshire, UK.

This recording's parameters are already specified in gypsum/radio_input.py::INPUT_SOURCES, making it straightforward to get gypsum up and running. The file should be placed in <gypsum_root>/vendored_signals/.