Indent subgraph sections

The two subgraph paragraphs below "Subgraphs" should be
indented below it.

packages/mermaid/src/docs/syntax/flowchart.md

@@ -404,7 +404,7 @@ flowchart TB
     end
 ```
 
-## flowcharts
+### flowcharts
 
 With the graphtype flowchart it is also possible to set edges to and from subgraphs as in the flowchart below.
 
@@ -425,7 +425,7 @@ flowchart TB
     two --> c2
 ```
 
-## Direction in subgraphs
+### Direction in subgraphs
 
 With the graphtype flowcharts you can use the direction statement to set the direction which the subgraph will render like in this example.