[docs] add lleaves to README

[StrikerRUS]

cc @siboehm

[siboehm]

I hadn't even posted about lleaves anywhere yet but you still found it :) Feel free to add it, it's well tested and supports most inference settings. I'm mostly working on getting even more performance especially for large batch settings.

[StrikerRUS]

I was surprised lleaves could beat Treelite!
Nice work! 👍

[jameslamb]

oh wow! Really interesting project, thanks.

[github-actions]

This pull request has been automatically locked since there has not been any recent activity since it was closed. To start a new related discussion, open a new issue at https://github.com/microsoft/LightGBM/issues including a reference to this.