update documentation

README.md

-# task_environment
+### Auxiliary package to formalise the cognitive training domain ### 
+
+#### Package:
+- the folder contains the following classes:
+    * cognitive_game_env.py defines the cognitive domain used in the IRL algorithm
+    * cognitive_game_vars.py defines the variables employed by the BNs
+    * environment.py defines the main rules of the cognitive exercise
+    * episode.py, class to initialise and store the episodes (s, a, s')
+    
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