Update description of FileDialog `filters` property

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

doc/classes/FileDialog.xml

@@ -70,7 +70,7 @@
 			The dialog's open or save mode, which affects the selection behavior. See [enum FileMode].
 		</member>
 		<member name="filters" type="PackedStringArray" setter="set_filters" getter="get_filters" default="PackedStringArray()">
-			The available file type filters. For example, this shows only [code].png[/code] and [code].gd[/code] files: [code]set_filters(PackedStringArray(["*.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(PackedStringArray(["*.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_overrides_title" type="bool" setter="set_mode_overrides_title" getter="is_mode_overriding_title" default="true">
 			If [code]true[/code], changing the [code]Mode[/code] property will set the window title accordingly (e.g. setting mode to [constant FILE_MODE_OPEN_FILE] will change the window title to "Open a File").