feat(neptune): high level constructs for db clusters and instances

packages/@aws-cdk/aws-neptune/README.md

@@ -9,10 +9,93 @@
 >
 > [CFN Resources]: https://docs.aws.amazon.com/cdk/latest/guide/constructs.html#constructs_lib
 
+![cdk-constructs: Experimental](https://img.shields.io/badge/cdk--constructs-experimental-important.svg?style=for-the-badge)
+
+> The APIs of higher level constructs in this module are experimental and under active development.
+> They are subject to non-backward compatible changes or removal in any future version. These are
+> not subject to the [Semantic Versioning](https://semver.org/) model and breaking changes will be
+> announced in the release notes. This means that while you may use them, you may need to update
+> your source code when upgrading to a newer version of this package.
+
 ---
 
 <!--END STABILITY BANNER-->
 
+## Starting a Neptune Database
+
+To set up a Neptune database, define a `DatabaseCluster`. You must always launch a database in a VPC. 
+
+```ts
+const cluster = new DatabaseCluster(this, 'Database', {
+  vpc,
+  instanceType: InstanceType.R5_LARGE
+});
+```
+
+By default only writer instance is provisioned with this construct.
+
+## Connecting
+
+To control who can access the cluster, use the `.connections` attribute. Neptune databases have a default port, so
+you don't need to specify the port:
+
+```ts
+cluster.connections.allowDefaultPortFromAnyIpv4('Open to the world');
+```
+
+The endpoints to access your database cluster will be available as the `.clusterEndpoint` and `.clusterReadEndpoint`
+attributes:
+
+```ts
+const writeAddress = cluster.clusterEndpoint.socketAddress;   // "HOSTNAME:PORT"
+```
+
+## Customizing parameters
+
+Neptune allows configuring database behavior by supplying custom parameter groups.  For more details, refer to the
+following link: <https://docs.aws.amazon.com/neptune/latest/userguide/parameters.html>
+
+```ts
+const clusterParams = new ClusterParameterGroup(this, 'ClusterParams', {
+  description: 'Cluster parameter group',
+  parameters: {
+    neptune_enable_audit_log: '1'
+  },
+});
+
+const dbParams = new ParameterGroup(this, 'DbParams', {
+  description: 'Db parameter group',
+  parameters: {
+    neptune_query_timeout: '120000'
+  },
+});
+
+const cluster = new DatabaseCluster(this, 'Database', {
+  vpc,
+  instanceType: InstanceType.R5_LARGE,
+  clusterParameterGroup: clusterParams,
+  parameterGroup: dbParams,
+});
+```
+
+## Adding replicas
+
+`DatabaseCluster` allows launching replicas along with the writer instance. This can be specified using the `instanceCount`
+attribute.
+
+```ts
+const cluster = new DatabaseCluster(this, 'Database', {
+  vpc,
+  instanceType: InstanceType.R5_LARGE,
+  instances: 2
+});
+```
+
+Additionally it is also possible to add replicas using `DatabaseInstance` for an existing cluster.
+
 ```ts
-import * as neptune from '@aws-cdk/aws-neptune';
+const replica1 = new DatabaseInstance(this, 'Instance', {
+  cluster,
+  instanceType: InstanceType.R5_LARGE
+});
 ```