enhance ParticleProcessMaterial.xml documentation

Signed-off-by: Saif Kandil <[email protected]>

doc/classes/ParticleProcessMaterial.xml

@@ -293,7 +293,7 @@
 			[b]Note:[/b] Animated velocities will not be affected by damping, use [member velocity_limit_curve] instead.
 		</member>
 		<member name="scale_curve" type="Texture2D" setter="set_param_texture" getter="get_param_texture">
-			Each particle's scale will vary along this [CurveTexture]. If a [CurveXYZTexture] is supplied instead, the scale will be separated per-axis.
+			Each particle's scale will vary along this [CurveTexture] over its lifetime. If a [CurveXYZTexture] is supplied instead, the scale will be separated per-axis.
 		</member>
 		<member name="scale_max" type="float" setter="set_param_max" getter="get_param_max" default="1.0">
 			Maximum initial scale applied to each particle.