[unitree] Add lead teleop documentation

[iory]

For unitree users, I added documentation for lead teleop.

[tkmtnt7000]

I am sorry and thank you very much for making leadteleop documentation. I think it’s ok.

[iory]

Thank you for the review!
Since @a-ichikura is the current core user, we will wait for her review from her perspective.

[a-ichikura]

Thank you for your editing the README.
If I understand correctly, the press Button colors and functions are slightly different.

Button Presses	LED Color	Action	Description
1 press	Blue	Sit	Unitree sits and will not walk.
2 presses	Green	Stand	Unitree stands up and is able to walk.
3 presses	Yellow	-	-
4 presses	White	Disable movement	Unitree stops moving.
5 presses	Purple	Enable movement	Unitree is able to move again.

*normal color is Red (the robot is just standing).

I cannot infer the 4 presses(yellow) function. What is it for?

[iory]

Button Presses	LED Color	Action	Description
0 presses	Red	no action	Unitree is just standing.
1 press	Blue	Sit	Unitree sits and will not walk.
2 presses	Green	Stand	Unitree stands up and is able to walk.
3 presses	Yellow	no action	no action
4 presses	White	Disable movement	Unitree stops moving.
5 presses	Purple	Enable movement	Unitree is able to move again.

Thank you. I fixed the table.

I cannot infer the 4 presses(yellow) function. What is it for?

The "3 presses" option is intentionally unassigned to prevent accidental presses since "4 presses" disables movement.