docs: update README

Author: evansims

README.md

@@ -125,27 +125,29 @@ let [can_edit, can_delete, can_share] = vault.batch_check(&[
 ]).await?[..] else { unreachable!() };
 ```
 
-## Authorization API
+## Usage
+
+### Authorization API
 
 ```rust
 let vault = client.organization("org_...").vault("vlt_...");
 ```
 
-### Permission Checks
+#### Permission Checks
 
 ```rust
 let allowed = vault.check("user:alice", "view", "doc:1").await?;
 ```
 
-### Relationships
+#### Relationships
 
 ```rust
 vault.relationships()
     .write(Relationship::new("document:readme", "viewer", "user:alice"))
     .await?;
 ```
 
-### Lookups
+#### Lookups
 
 ```rust
 let docs = vault.resources()
@@ -157,21 +159,21 @@ let docs = vault.resources()
 
 See the [Authorization API Guide](docs/guides/authorization-api.md) for ABAC context, batch checks, explain, simulate, watch, and more.
 
-## Management API
+### Management API
 
 ```rust
 let org = client.organization("org_...");
 ```
 
-### Vaults
+#### Vaults
 
 ```rust
 let vault = org.vaults()
     .create(CreateVaultRequest::new("production"))
     .await?;
 ```
 
-### Schemas
+#### Schemas
 
 ```rust
 vault.schemas().push(r#"
@@ -184,7 +186,7 @@ type document {
 "#).await?;
 ```
 
-### Members & Teams
+#### Members & Teams
 
 ```rust
 org.members()
@@ -196,7 +198,7 @@ org.teams()
     .await?;
 ```
 
-### Audit Logs
+#### Audit Logs
 
 ```rust
 let events = org.audit().list().collect().await?;