Add retrieve example for the extended attribute

in the virtual extended attribute there is the following example

collection.lookupIn(

    "airport_1254",

    Collections.singletonList(

        LookupInSpec.get(LookupInMacro.EXPIRY_TIME).xattr())

);

for clarity please add the following like that demonstrate the retrieval process.

System.out.println(res.contentAs(0, String.class));

you may also add which features are available currently with the macro

Reporter: Roi Katz
E-mail: roi.katz@Couchbase.com