mir_dwb_critics: Fill in description

mir_dwb_critics/default_critics.xml

@@ -4,7 +4,7 @@
       <description>Scores trajectories based on how far along the global path they end up.</description>
     </class>
     <class type="mir_dwb_critics::PathAngleCritic" base_class_type="dwb_local_planner::TrajectoryCritic">
-      <description>TODO</description>
+      <description>Scores trajectories based on the difference between the path's current angle and the trajectory's angle</description>
     </class>
     <class type="mir_dwb_critics::PathDistPrunedCritic" base_class_type="dwb_local_planner::TrajectoryCritic">
       <description>Scores trajectories based on the distance to the global path, only taking the parts into account that are still ahead of the robot.</description>