Update readme for using new/flexible interfaces

README.md

@@ -119,6 +119,22 @@ function makeId(length) {
 
 ```
 
+### Exists test
+
+```js
+import xk6_couchbase from 'k6/x/couchbase';
+
+
+const client = xk6_couchbase.newClient('localhost', '<username>', '<password>');
+export default () => {
+    // syntax :: client.exists("<db>", "<scope>", "<keyspace>", "<docId>");
+    var res = client.exists("test", "_default", "_default", "002wPJwiJArcUpz");
+    console.log(res);
+}
+
+```
+
+
 ### FindOne test
 
 ```js