add customize db config to README.md (#402)

README.md

@@ -99,6 +99,15 @@ public class AppConfiguration extends AbstractDocumentDbConfiguration {
     }
 }
 ```
+Or if you want to customize your config:
+```java
+public DocumentDBConfig getConfig() {
+    DocumentDBConfig dbConfig = DocumentDBConfig.builder(uri, key, dbName).build();
+    dbConfig.getConnectionPolicy().setConnectionMode(ConnectionMode.DirectHttps);
+    dbConfig.getConnectionPolicy().setMaxPoolSize(1000);
+    return dbConfig;
+}
+```
 By default, `@EnableDocumentDbRepositories` will scan the current package for any interfaces that extend one of Spring Data's repository interfaces. Using it to annotate your Configuration class to scan a different root package by type if your project layout has multiple projects and it's not finding your repositories.
 ```java
 @Configuration