[docs] Fix description of follow component logic (aframevr#5423)

Previously, the docs suggested calculating a direction based on the difference between the target position and the follower's direction. However, this would not yield the direction from the follower to the target.

The updated documentation suggests subtracting the follower's position from the target position, which is the correct logic and matches the code following the description.

docs/introduction/writing-a-component.md

@@ -688,7 +688,7 @@ scene uptime as `time` and time since the last frame as `timeDelta` into the
 far the entity should travel towards the target this frame, given the speed.
 
 To calculate the direction the entity should head in, we subtract the entity's
-position vector from the target entity's direction vector. We have access to
+position vector from the target entity's position vector. We have access to
 the entities' three.js objects via `.object3D`, and from there the position
 vector `.position`. We store the direction vector in the `this.directionVec3`
 we previously allocated in the `init()` handler.