Update PlatformerTrajectory description

Author: 4ian

extensions/reviewed/PlatformerTrajectory.json

@@ -11,7 +11,7 @@
   "shortDescription": "Platformer character jump easy configuration and platformer AI tools.",
   "version": "0.1.0",
   "description": [
-    "This extension allows to:",
+    "For objects having the 2D platformer character behavior, this provides a behavior allowing to:",
     "* Configure the height of a jump by automatically choosing the right jump speed ([open the project online](https://editor.gdevelop.io/?project=example://platformer-jump-evaluator)).",
     "* Know when to jump to reach a platform (can be useful for AI).",
     "* Draw jump trajectories to check a level design."
@@ -1180,4 +1180,4 @@
     }
   ],
   "eventsBasedObjects": []
-}
+}