Added information about input normalization to the best practices doc (#220)

docs/best-practices.md

 ## States
 * States should include all variables relevant to allowing the agent to take the optimally informed decision.
 * Categorical state variables such as type of object (Sword, Shield, Bow) should be encoded in one-hot fashion (ie `3` -> `0, 0, 1`).
-* Rotation information on GameObjects should be recorded as `state.Add(transform.rotation.eulerAngles.y/180.0f-1.0f);` rather than `state.Add(transform.rotation.y);`. 
+* Besides encoding non-numeric values, all inputs should be normalized to be in the range 0 to +1 (or -1 to 1). For example rotation information on GameObjects should be recorded as `state.Add(transform.rotation.eulerAngles.y/180.0f-1.0f);` rather than `state.Add(transform.rotation.y);`. See the equation below for one approach of normaliztaion. 
+
+![normalization](../images/normalization.png)
 
 ## Actions
 * When using continuous control, action values should be clipped to an appropriate range.