Readme updates

README.md

@@ -1,40 +1,53 @@
 # Checked AWS Custom Resource
 
-This is a wrapper around the AWS CDK's [AwsCustomResource](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_custom-resources.AwsCustomResource.html), which complains when you give it SDK services or actions which don't exist.
+This is a wrapper around the AWS CDK's [AwsCustomResource](https://docs.aws.amazon.com/cdk/api/latest/docs/@aws-cdk_custom-resources.AwsCustomResource.html).
+
+By default, if you specify an SDK function for `AwsCustomResource` which doens't exist, CDK will still generate a
+CloudFormation template for you and attempt to deploy it, just to eventually fail.
+
+This wrapper resolves that by complaining when you give it SDK services or actions which don't exist. The price is fairly small:
+your CDK project will depend on `aws-sdk`.
 
 To install
 
 ```
     npm install --save checked-aws-custom-resource
 ```
 
-For example, this is fine:
+For example, this is fine.
 
 ```ts
 new CheckedAwsCustomResource(stack, "Good", {
   onCreate: {
     service: "RDS",
     action: "modifyDBCluster",
-    parameters: {},
+    parameters: {
+      DBClusterIdentifier: db.ref,
+      EnableHttpEndpoint: true
+    },
     physicalResourceId: `resourceId`
   }
 });
 ```
 
-but if you get the capitalization wrong, it will fail during instantiation.
+Meanwhile, here the captilization of "ModifyDBCluster" is wrong, so
+the class will throw an exception during instantiation:
 
 ```ts
-new CheckedAwsCustomResource(stack, "Good", {
+new CheckedAwsCustomResource(stack, "Bad", {
   onCreate: {
     service: "RDS",
     action: "ModifyDBCluster",
-    parameters: {},
+    parameters: {
+      DBClusterIdentifier: db.ref,
+      EnableHttpEndpoint: true
+    },
     physicalResourceId: `resourceId`
   }
 });
 ```
 
-If this is in your Stack when you `synth` it, you'll see:
+If this is in your Stack when you `cdk synth` it, you'll see a helpful error message.
 
 ```
     $ cdk synth MyStack

package.json

@@ -1,6 +1,6 @@
 {
   "name": "checked-aws-custom-resource",
-  "version": "0.1.5",
+  "version": "0.1.6",
   "main": "src/index.js",
   "scripts": {
     "test": "jest tests/test.ts",