doc: fix typo in ARCHITECTURE.md (googleapis#14471)

Author: cuiy0006

ARCHITECTURE.md

@@ -107,8 +107,8 @@ defined, there are separate `${library}::*Client` objects.
 
 These are some examples:
 
-- Bigtable has a [`bigtable::Table`](/google/cloud/bigtable/table.h) client. It
-  also has two admin clients:
+- Bigtable has a [`bigtable::DataClient`](/google/cloud/bigtable/data_client.h)
+  client. It also has two admin clients:
   [`bigtable_admin::BigtableInstanceAdminClient`](/google/cloud/bigtable/admin/bigtable_instance_admin_client.h)
   and
   [`bigtable_admin::BigtableTableAdminClient`](/google/cloud/bigtable/admin/bigtable_table_admin_client.h).