`obs_type="env_state"` is not a valid option; `obs_type="state"` is not yet supported?

[EricCousineau-TRI]

first off, thanks for putting this together!

docs mention using obs_type="env_state"; however, code does not have that listed:

gym-aloha/gym_aloha/env.py

Lines 46 to 84 in 7f19312

	if self.obs_type == "state":
	raise NotImplementedError()
	self.observation_space = spaces.Box(
	low=np.array([0] * len(JOINTS)), # ???
	high=np.array([255] * len(JOINTS)), # ???
	dtype=np.float64,
	)
	elif self.obs_type == "pixels":
	self.observation_space = spaces.Dict(
	{
	"top": spaces.Box(
	low=0,
	high=255,
	shape=(self.observation_height, self.observation_width, 3),
	dtype=np.uint8,
	)
	}
	)
	elif self.obs_type == "pixels_agent_pos":
	self.observation_space = spaces.Dict(
	{
	"pixels": spaces.Dict(
	{
	"top": spaces.Box(
	low=0,
	high=255,
	shape=(self.observation_height, self.observation_width, 3),
	dtype=np.uint8,
	)
	}
	),
	"agent_pos": spaces.Box(
	low=-1000.0,
	high=1000.0,
	shape=(len(JOINTS),),
	dtype=np.float64,
	),
	}
	)

but then running

gym.make("gym_aloha/AlohaInsertion-v0", obs_type="state")

throws NotImplementedError

consider updating README docs for time being?