Add documentation for GpuParticles2D collisions

doc/classes/GPUParticles2D.xml

@@ -5,7 +5,8 @@
 	</brief_description>
 	<description>
 		2D particle node used to create a variety of particle systems and effects. [GPUParticles2D] features an emitter that generates some number of particles at a given rate.
-		Use the [code]process_material[/code] property to add a [ParticleProcessMaterial] to configure particle appearance and behavior. Alternatively, you can add a [ShaderMaterial] which will be applied to all particles.
+		Use the [member process_material] property to add a [ParticleProcessMaterial] to configure particle appearance and behavior. Alternatively, you can add a [ShaderMaterial] which will be applied to all particles.
+		2D particles can optionally collide with [LightOccluder2D] nodes (note: they don't collide with [PhysicsBody2D] nodes).
 	</description>
 	<tutorials>
 		<link title="Particle systems (2D)">$DOCS_URL/tutorials/2d/particle_systems_2d.html</link>
@@ -42,6 +43,7 @@
 			Number of particles emitted in one emission cycle.
 		</member>
 		<member name="collision_base_size" type="float" setter="set_collision_base_size" getter="get_collision_base_size" default="1.0">
+			Multiplier for particle's collision radius. [code]1.0[/code] corresponds to the size of the sprite.
 		</member>
 		<member name="draw_order" type="int" setter="set_draw_order" getter="get_draw_order" enum="GPUParticles2D.DrawOrder" default="1">
 			Particle draw order. Uses [enum DrawOrder] values.

doc/classes/ParticleProcessMaterial.xml

@@ -123,7 +123,8 @@
 		</member>
 		<member name="collision_mode" type="int" setter="set_collision_mode" getter="get_collision_mode" enum="ParticleProcessMaterial.CollisionMode" default="0">
 			The particles' collision mode.
-			[b]Note:[/b] Particles can only collide with [GPUParticlesCollision3D] nodes, not [PhysicsBody3D] nodes. To make particles collide with various objects, you can add [GPUParticlesCollision3D] nodes as children of [PhysicsBody3D] nodes.
+			[b]Note:[/b] 3D Particles can only collide with [GPUParticlesCollision3D] nodes, not [PhysicsBody3D] nodes. To make particles collide with various objects, you can add [GPUParticlesCollision3D] nodes as children of [PhysicsBody3D] nodes.
+			[b]Note:[/b] 2D Particles can only collide with [LightOccluder2D] nodes, not [PhysicsBody2D] nodes.
 		</member>
 		<member name="collision_use_scale" type="bool" setter="set_collision_use_scale" getter="is_collision_using_scale" default="false">
 			Should collision take scale into account.