Improve explenation for Trigger and Capture update modes (#5476)

Co-authored-by: Hugo Locurcio <[email protected]>

tutorials/animation/introduction.rst

@@ -231,11 +231,17 @@ mode, track interpolation, and loop mode.
 The update mode of a track tells Godot when to update the property
 values. This can be:
 
--  Continuous: Update the property on each frame
--  Discrete: Only update the property on keyframes
--  Trigger: Only update the property on keyframes or triggers
--  Capture: Remember the current value of the property, and blend it with the
-   first animation key
+-  **Continuous:** Update the property on each frame
+-  **Discrete:** Only update the property on keyframes
+-  **Trigger:** Only update the property on keyframes or triggers.
+   Triggers are a type of keyframe used by the
+   ``current_animation`` property of a :ref:`class_AnimationPlayer`,
+   and Animation Playback tracks.
+-  **Capture:** if the first keyframe's time is greater than ``0.0``, the
+   current value of the property will be remembered and
+   will be blended with the first animation key. For example, you
+   could use the Capture mode to move a node that's located anywhere
+   to a specific location.
 
 .. figure:: img/animation_track_rate.png
    :alt: Track mode