Fixed some typos in README.md

README.md

@@ -38,7 +38,7 @@ located by CMake.
 
 ## Practical considerations
 
-From a user point of view, one should be concerned exclusively with the `Planner`
+From a user point of view, one should be concerned exclusively about the `Planner`
 abstract class declared in `src/imagine-planner.h`:
 
 ```c++
@@ -64,7 +64,7 @@ Planner implementations inherit from the `Planner` abstract class, providing a
 definition for the function operator. A `Plan` consists of several `Step`s, being
 one `Step` an operator and the state that is expected after the execution of this operator.
 
-`PlanState` and `GoalSpecification` objects are simply collection of Predicates.
+`PlanState` and `GoalSpecification` objects are simply collections of Predicates.
 The `Domain`'s instances are created providing the path and version of an ADES
 database. Internally, the constructor method will read the whole database and
 translate the operators' specifications into the internal representation of the