Add READMEs to hash algorithms/polynomial interp.

algorithms/hash_algorithms/README.md
	-Add a README listing the algorithms implemented (and the
	corresponding file for each).

algorithms/polynomial_interpolation/README.md
	-Add a README describing what the project implemented, how
	functionality is divided between `polynomial_interpolation.py`
	and `animation.py`; link the three gifs in `animation/`.