Update description of FileDialog `filters` property

specify that multiple filetypes/extensions can be included in one filter within the
PackedStringArray, and provide an example

(cherry picked from commit 123cfb4759076786f783f59becf3eaac26059e45)

doc/classes/FileDialog.xml

@@ -65,7 +65,7 @@
 		</member>
 		<member name="dialog_hide_on_ok" type="bool" setter="set_hide_on_ok" getter="get_hide_on_ok" override="true" default="false" />
 		<member name="filters" type="PoolStringArray" setter="set_filters" getter="get_filters" default="PoolStringArray(  )">
-			The available file type filters. For example, this shows only [code].png[/code] and [code].gd[/code] files: [code]set_filters(PoolStringArray(["*.png ; PNG Images","*.gd ; GDScript Files"]))[/code].
+			The available file type filters. For example, this shows only [code].png[/code] and [code].gd[/code] files: [code]set_filters(PoolStringArray(["*.png ; PNG Images","*.gd ; GDScript Files"]))[/code]. Multiple file types can also be specified in a single filter. [code]"*.png, *.jpg, *.jpeg ; Supported Images"[/code] will show both PNG and JPEG files when selected.
 		</member>
 		<member name="mode" type="int" setter="set_mode" getter="get_mode" enum="FileDialog.Mode" default="4">
 			The dialog's open or save mode, which affects the selection behavior. See enum [code]Mode[/code] constants.