Update Elasticsearch documentation with authentication information (#5381)

- Add documentation to show how to supply credential to access a
  secured elasticsearch server.

Fixes #5329

docs/bucket/notifications/README.md

@@ -271,7 +271,7 @@ The default location of Minio server configuration file is ``~/.minio/config.jso
 |:---|:---|:---|
 | `enable` | _bool_ | (Required) Is this server endpoint configuration active/enabled? |
 | `format` | _string_ | (Required) Either `namespace` or `access`. |
-| `url` | _string_ | (Required) The Elasticsearch server's address. For example: `http://localhost:9200`. |
+| `url` | _string_ | (Required) The Elasticsearch server's address, with optional authentication info. For example: `http://localhost:9200` or with authentication info `http://elastic:MagicWord@127.0.0.1:9200`. |
 | `index` | _string_ | (Required) The name of an Elasticsearch index in which Minio will store documents. |
 
 An example of Elasticsearch configuration is as follows:
@@ -287,6 +287,8 @@ An example of Elasticsearch configuration is as follows:
 },
 ```
 
+If Elasticsearch has authentication enabled, the credentials can be supplied to Minio via the `url` parameter formatted as `PROTO://USERNAME:PASSWORD@ELASTICSEARCH_HOST:PORT`.
+
 After updating the configuration file, restart the Minio server to put the changes into effect. The server will print a line like `SQS ARNs:  arn:minio:sqs::1:elasticsearch` at start-up if there were no errors.
 
 Note that, you can add as many Elasticsearch server endpoint configurations as needed by providing an identifier (like "1" in the example above) for the Elasticsearch instance and an object of per-server configuration parameters.