[mutter] Add document sections

[Jonas Ådahl <jadahl src gnome org>]

commit d7a4c659344846d57d78a1775c31b9008f5be024
Author: Jonas Ådahl <jadahl gmail com>
Date:   Sun Oct 11 13:32:21 2020 +0000

    Add document sections

 Compositor-stage-and-hardware-relationships.md | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/Compositor-stage-and-hardware-relationships.md b/Compositor-stage-and-hardware-relationships.md
index 7afb736..33da80a 100644
--- a/Compositor-stage-and-hardware-relationships.md
+++ b/Compositor-stage-and-hardware-relationships.md
@@ -5,7 +5,7 @@
  - `MetaOuptut` is a connector e.g. a DisplayPort connector or HDMI connector.
  - `MetaCrtc` represents a component on the display hardware that channels video memory to connectors.
 
-Entity relationship diagram:
+### Entity relationship diagram
 
 ```mermaid
 erDiagram
@@ -24,6 +24,8 @@ erDiagram
   ClutterStageView ||--|| ClutterFrameClock : owns
 ```
 
+### Class diagrams
+
 `MetaBackend`, `MetaGpu` and `MetaMonitorManager` class diagrams.
 
 ```mermaid