Add description for the environments

[Jialn]

To unify name style of all the environments, I changed name of simple navigation form "...NoLanguage" to "...WithLanguage".

[le-horizon]

Since it's for the public, maybe add a section on minimum system requirements e.g. ubuntu version?

Alf pybullet humanoid walking seems like the robot has arm injury and is running to get help. Maybe a better gif if easy to generate :)

[Jialn]

Repo is called "SocialRobot", but directory structure and env names use "social_bot". If easy to do, let's keep them consistent?

Yes, and the path is a little bit long, Maybe "python/social_bot/" -> "socialrobot" or "social_robot" ? @le-horizon @emailweixu