Update Learning-Environment-Create-New.md (#2925)

Added a missing instruction in the Final Editor Setup section.

docs/Learning-Environment-Create-New.md

 2. Change **Decision Interval** from `1` to `10`.
 3. Drag the Target GameObject from the Hierarchy window to the RollerAgent
     Target field.
-4. Modify the Behavior Parameters of the Agent :
+4. Add the Behavior Parameters script with the Add Component button from the RollerAgent Inspector.
+5. Modify the Behavior Parameters of the Agent :
   * `Behavior Name` to *RollerBallBrain*
   * `Vector Observation` `Space Size` = 8
   * `Vector Action` `Space Type` = **Continuous**