Update usage section with proper inference example

Full training details: optimizer, schedule, results, hardware

Upload finished 350M PG-19 checkpoint (step 50000)

Link inference repo and fix checkpoint filename

Remove intermediate 5k step checkpoint

Fix training steps: 50k not 5k

Upload 350M PG-19 byte-level SEDD checkpoint (step 5000)

Update README for 350M PG-19 byte-level SEDD checkpoint

Remove old synth checkpoint

Upload synth_step_60000.pth with huggingface_hub

initial commit