Update README.md ?

[yuvaltassa]

Hi folks !

Yuval here from the MuJoCo development team.
Not sure if this project is still maintained, but you README has the curious pointer

3.  Download mjpro210 from roboti.us [here](https://mujoco.org/download)
4.  Put mjpro210 in a `.mujoco` directory in your home directory
5.  `make`

Either you only support mujoco200, in which case you want to send people to roboti, or you support more recent versions, in which case you should indeed send people to our download page (or tell them to clone it, as MuJoCo is now fully open-source 🎉 – don't do that, better to pin to a version)