make nested documentation pages appear in the sidebar

docs/api/create-state-accessing.md

@@ -3,6 +3,7 @@ layout: default
 title: Accessing and updating state
 nav_order: 1
 parent: createState
+grand_parent: API
 ---
 
 ## Accessing and updating state

docs/api/create-state-component-bindings.md

@@ -3,6 +3,7 @@ layout: default
 title: Component bindings
 nav_order: 2
 parent: createState
+grand_parent: API
 ---
 
 ## Component bindings

docs/api/create-state-deriving.md

@@ -3,6 +3,7 @@ layout: default
 title: Deriving state
 nav_order: 3
 parent: createState
+grand_parent: API
 ---
 
 ## Deriving state

docs/api/create-state-equality.md

@@ -3,6 +3,7 @@ layout: default
 title: Equality and update control
 nav_order: 4
 parent: createState
+grand_parent: API
 ---
 
 ## Equality and update control