Add detail to emitting docs for particles

doc/classes/CPUParticles2D.xml

@@ -169,7 +169,7 @@
 			The sphere's radius if [member emission_shape] is set to [constant EMISSION_SHAPE_SPHERE].
 		</member>
 		<member name="emitting" type="bool" setter="set_emitting" getter="is_emitting" default="true">
-			If [code]true[/code], particles are being emitted.
+			If [code]true[/code], particles are being emitted. [member emitting] can be used to start and stop particles from emitting. However, if [member one_shot] is [code]true[/code] setting [member emitting] to [code]true[/code] will not restart the emission cycle until after all active particles finish processing. You can use the [signal finished] signal to be notified once all active particles finish processing.
 		</member>
 		<member name="explosiveness" type="float" setter="set_explosiveness_ratio" getter="get_explosiveness_ratio" default="0.0">
 			How rapidly particles in an emission cycle are emitted. If greater than [code]0[/code], there will be a gap in emissions before the next cycle begins.

doc/classes/CPUParticles3D.xml

@@ -183,7 +183,7 @@
 			The sphere's radius if [enum EmissionShape] is set to [constant EMISSION_SHAPE_SPHERE].
 		</member>
 		<member name="emitting" type="bool" setter="set_emitting" getter="is_emitting" default="true">
-			If [code]true[/code], particles are being emitted.
+			If [code]true[/code], particles are being emitted. [member emitting] can be used to start and stop particles from emitting. However, if [member one_shot] is [code]true[/code] setting [member emitting] to [code]true[/code] will not restart the emission cycle until after all active particles finish processing. You can use the [signal finished] signal to be notified once all active particles finish processing.
 		</member>
 		<member name="explosiveness" type="float" setter="set_explosiveness_ratio" getter="get_explosiveness_ratio" default="0.0">
 			How rapidly particles in an emission cycle are emitted. If greater than [code]0[/code], there will be a gap in emissions before the next cycle begins.

doc/classes/GPUParticles2D.xml

@@ -50,7 +50,7 @@
 			Particle draw order. Uses [enum DrawOrder] values.
 		</member>
 		<member name="emitting" type="bool" setter="set_emitting" getter="is_emitting" default="true">
-			If [code]true[/code], particles are being emitted.
+			If [code]true[/code], particles are being emitted. [member emitting] can be used to start and stop particles from emitting. However, if [member one_shot] is [code]true[/code] setting [member emitting] to [code]true[/code] will not restart the emission cycle until after all active particles finish processing. You can use the [signal finished] signal to be notified once all active particles finish processing.
 		</member>
 		<member name="explosiveness" type="float" setter="set_explosiveness_ratio" getter="get_explosiveness_ratio" default="0.0">
 			How rapidly particles in an emission cycle are emitted. If greater than [code]0[/code], there will be a gap in emissions before the next cycle begins.

doc/classes/GPUParticles3D.xml

@@ -78,7 +78,7 @@
 		<member name="draw_skin" type="Skin" setter="set_skin" getter="get_skin">
 		</member>
 		<member name="emitting" type="bool" setter="set_emitting" getter="is_emitting" default="true">
-			If [code]true[/code], particles are being emitted.
+			If [code]true[/code], particles are being emitted. [member emitting] can be used to start and stop particles from emitting. However, if [member one_shot] is [code]true[/code] setting [member emitting] to [code]true[/code] will not restart the emission cycle until after all active particles finish processing. You can use the [signal finished] signal to be notified once all active particles finish processing.
 		</member>
 		<member name="explosiveness" type="float" setter="set_explosiveness_ratio" getter="get_explosiveness_ratio" default="0.0">
 			Time ratio between each emission. If [code]0[/code], particles are emitted continuously. If [code]1[/code], all particles are emitted simultaneously.