readme.md: Use `on_finish(result, error)` callback signature
readme.md: Use `on_finish(result, error)` callback signature

nmrugg/LZMA-JS,nmrugg/LZMA-JS,addaleax/LZMA-JS,nmrugg/LZMA-JS,addaleax/LZMA-JS,addaleax/LZMA-JS