fix: Updating README.md sample

Author: steve-calvert-glean

README.md

@@ -15,15 +15,17 @@ Each namespace has its own authentication requirements and access patterns. Whil
 ```java
 // Example of accessing Client namespace
 Glean glean = Glean.builder()
-        .bearerAuth("client-token")
+        .apiToken("client-token")
+        .instance("instance-name")
         .build();
 glean.client().search().query()
         .searchRequest(SearchRequest.builder().query("search term").build())
         .call();
 
 // Example of accessing Indexing namespace 
 Glean glean = Glean.builder()
-        .bearerAuth("indexing-token")
+        .apiToken("indexing-token")
+        .instance("instance-name")
         .build();
 glean.indexing().documents().index()
         .request(DocumentBulkIndexRequest.builder() /* document data */ .build())