readme: document why output sizes are required for non-streaming APIs
readme: document why output sizes are required for non-streaming APIs
terrelln/python-zstandard,indygreg/python-zstandard,terrelln/python-zstandard,indygreg/python-zstandard,indygreg/python-zstandard,terrelln/python-zstandard,terrelln/python-zstandard,indygreg/python-zstandard