Update README.md

Author: davidyaha

README.md

@@ -1,6 +1,5 @@
 # graphql-redis-subscriptions
 
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 This package implements the PubSubEngine Interface from the [graphql-subscriptions](https://github.com/apollographql/graphql-subscriptions) package and also the new AsyncIterator interface. 
@@ -109,7 +108,39 @@ export const resolvers = {
 }
 ```
 
-## Creating the Redis Client
+## Configuring RedisPubSub
+
+`RedisPubSub` constructor can be passed a configuration object to enable some advanced features. 
+
+```ts
+export interface PubSubRedisOptions {
+  connection?: RedisOptions | string;
+  triggerTransform?: TriggerTransform;
+  connectionListener?: (err?: Error) => void;
+  publisher?: RedisClient;
+  subscriber?: RedisClient;
+  reviver?: Reviver;
+  serializer?: Serializer;
+  deserializer?: Deserializer;
+  messageEventName?: string;
+  pmessageEventName?: string;
+}
+```
+
+| option | type | default | description |
+| ------ | ---- | ------- | ----------- |
+| `connection` | [`object \| string`](https://github.com/luin/ioredis#connect-to-redis) | `undefined` | the connection option is passed as is to the `ioredis` constructor to create redis subscriber and publisher instances. for greater controll, use `publisher` and `subscriber` options. |
+| `triggerTransform` | `function` | (trigger) => trigger | [deprecated](#using-trigger-transform-deprecated) |
+| `connectionListener` | `function` | `undefined` | pass in connection listener to log errors or make sure connection to redis instance was created successfully. |
+| `publisher` | `function` | `undefined` | must be passed along side `subscriber`. see [#creating-a-redis-client](#creating-a-redis-client) |
+| `subscriber` | `function` | `undefined` | must be passed along side `publisher`. see [#creating-a-redis-client](#creating-a-redis-client) |
+| `reviver` | `function` | `undefined` | see [#using-a-custom-reviver](#using-a-custom-reviver) |
+| `serializer` | `function` | `undefined` | see [#using-a-custom-serializerdeserializer](#using-a-custom-serializerdeserializer) |
+| `deserializer` | `function` | `undefined` | see [#using-a-custom-serializerdeserializer](#using-a-custom-serializerdeserializer) |
+| `messageEventName` | `string` | `undefined` | see [#receiving-messages-as-buffers](#receiving-messages-as-buffers) |
+| `pmessageEventName` | `string` | `undefined` | see [#receiving-messages-as-buffers](#receiving-messages-as-buffers) |
+
+## Creating a Redis Client
 
 The basic usage is great for development and you will be able to connect to a Redis server running on your system seamlessly. For production usage, it is recommended to pass a redis client (like ioredis) to the RedisPubSub constructor. This way you can control all the options of your redis connection, for example the connection retry strategy.
 
@@ -133,7 +164,7 @@ const pubsub = new RedisPubSub({
 });
 ```
 
-**Receiving messages as Buffers**
+### Receiving messages as Buffers
 
 Some Redis use cases require receiving binary-safe data back from redis (in a Buffer). To accomplish this, override the event names for receiving messages and pmessages.  Different redis clients use different names, for example: