Update README.md: fixed --tp which is invalid is launch option

[didier-durand]

Hi,
As https://github.com/sgl-project/sglang/blob/main/python/sglang/srt/server_args.py at line 497 and next, --tp is not a valid command option.

Possible values --tensor-parallel-size or --tp-size

I chose --tensor-parallel-size to remain consistent with previous command suggested by this README

[hiSandog]

Confirmed — --tp isn't a valid option for sglang.launch_server; SGLang exposes the short --tp-size and the long --tensor-parallel-size, so the current README command would fail at startup. Using --tensor-parallel-size here also matches the vllm serve ... --tensor-parallel-size 2 line just above, which is a nice consistency win.

One thing worth double-checking before merge: that --tensor-parallel-size is indeed the spelling the SGLang version the README targets accepts (the flag surface has shifted between SGLang releases). If there's any doubt, --tp-size is the safer canonical short form.