Update Readme with MDP/POMDP and Discrete/Continuous information

[Omastto1]

I think that a table with a basic problem description would greatly improve the package.

Something like the following:

MDPs

problem	space	action
GridWorld 3x3	Discrete	Discrete

POMDPS

problem	space	action	observation
MiniHallway	Discrete	Discrete	Discrete

I Will create a draft sometime in the future, I guess.

PS: This could also be extended with Deterministic / Stochastic actions / observations and state / action / observation space size.

[zsunberg]

Yes, this would be great!