Fix documentation of Mask2D. (#8)

* Fix documentation of Mask2D.

* timestamp is now stamp.

moveit_studio_msgs/moveit_studio_vision_msgs/msg/Mask2D.msg

@@ -5,13 +5,12 @@
 
 # The position of the top-left corner of the mask within the segmented image. 
 # (0, 0) is the top-left corner of the segmented image.
-# The segmented image should be referenced in the containing image segmenter
-# message.
 int32 x
 int32 y
 
 # A single plane image with the mask pixels.
 # The image pixels can be encoded as:
 #   - Integer: only non-zero pixels belong to the mask.
 #   - Floating point: each pixel has a probability of belonging to the mask.
+# The stamp and frame_id of the mask image header match those of the segmented image header.
 sensor_msgs/Image pixels