Clarify filtering by node type and group in the Scene tree dock

This functionality has been available since 4.0, but was difficult
to discover since there was no tooltip and the placeholder didn't
mention it.

editor/scene_tree_dock.cpp

@@ -3841,7 +3841,8 @@ SceneTreeDock::SceneTreeDock(Node *p_scene_root, EditorSelection *p_editor_selec
 	// The "Filter Nodes" text input above the Scene Tree Editor.
 	filter = memnew(LineEdit);
 	filter->set_h_size_flags(SIZE_EXPAND_FILL);
-	filter->set_placeholder(TTR("Filter Nodes"));
+	filter->set_placeholder(TTR("Filter: name, t:type, g:group"));
+	filter->set_tooltip_text(TTR("Filter nodes by entering a part of their name, type (if prefixed with \"type:\" or \"t:\")\nor group (if prefixed with \"group:\" or \"g:\"). Filtering is case-insensitive."));
 	filter_hbc->add_child(filter);
 	filter->add_theme_constant_override("minimum_character_width", 0);
 	filter->connect("text_changed", callable_mp(this, &SceneTreeDock::_filter_changed));