Update cpp/rat.cpp

Co-authored-by: Alex H. Room <69592136+alexhroom@users.noreply.github.com>

Author: StephenNneji

cpp/rat.cpp

@@ -610,7 +610,7 @@ const std::string docsRATMain = R"(Entry point for the main reflectivity computa
 Parameters
 ----------
 problem_def : Rat.rat_core.ProblemDefinition
-    The problem input for the RAT calculation.
+    The project input for the RAT calculation.
 limits : RATapi.rat_core.Limits
     Min and max values for each parameter defined in the problem definition.
 control : RATapi.rat_core.Control