docs(README): add explanation about using the library option with TS

Author: naorpeled

README.md

@@ -103,7 +103,7 @@ let results = await query('SELECT * FROM table WHERE name = ?', ['serverless'])
 let results = await query({
   sql: 'SELECT * FROM table WHERE name = ?',
   timeout: 10000,
-  values: ['serverless'])
+  values: ['serverless']
 })
 ```
 
@@ -206,6 +206,26 @@ Set your own mysql library, wrapped with AWS x-ray for instance
 library: require('aws-sdk-xray-node')(require('mysql'));
 ```
 
+### Consideration when using TypeScript
+Currently, our type definitions rely on the `mysql` module.
+In order to use a custom library, you will need to do something along the following snippet:
+
+```typescript
+import * as serverlessMysql from 'serverless-mysql';
+import * as mysql2 from 'mysql2';
+
+const slsMysql = serverlessMysql({
+  library: mysql2 as any
+})
+
+// OR
+
+const slsMysql2 = serverlessMysql({
+  // @ts-ignore
+  library: mysql2
+})
+```
+
 ## Events
 The module fires seven different types of events: `onConnect`, `onConnectError`, `onRetry`, `onClose`, `onError`, `onKill`, and `onKillError`. These are *reporting* events that allow you to add logging or perform additional actions. You could use these events to short-circuit your handler execution, but using `catch` blocks is preferred. For example, `onError` and `onKillError` are not fatal and will be handled by `serverless-mysql`. Therefore, they will **NOT** `throw` an error and trigger a `catch` block.