add refrence (#36994)

* add refrence

* format

paddle/fluid/framework/fleet/heter_ps/cudf/concurrent_unordered_map.cuh.h

@@ -12,6 +12,10 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
+ *
+ * This source code refers to https://github.com/rapidsai/cudf
+ * and is licensed under the license found in the LICENSE file
+ * in the root directory of this source tree.
  */
 
 #ifndef CONCURRENT_UNORDERED_MAP_CUH

paddle/fluid/framework/fleet/heter_ps/cudf/hash_functions.cuh

@@ -12,6 +12,10 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
+ *
+ * This source code refers to https://github.com/rapidsai/cudf
+ * and is licensed under the license found in the LICENSE file
+ * in the root directory of this source tree.
  */
 
 #ifndef HASH_FUNCTIONS_CUH

paddle/fluid/framework/fleet/heter_ps/cudf/managed.cuh

@@ -12,6 +12,10 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
+ *
+ * This source code refers to https://github.com/rapidsai/cudf
+ * and is licensed under the license found in the LICENSE file
+ * in the root directory of this source tree.
  */
 
 #ifndef MANAGED_CUH

paddle/fluid/framework/fleet/heter_ps/cudf/managed_allocator.cuh

@@ -12,6 +12,10 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
+ *
+ * This source code refers to https://github.com/rapidsai/cudf
+ * and is licensed under the license found in the LICENSE file
+ * in the root directory of this source tree.
  */
 
 #ifndef MANAGED_ALLOCATOR_CUH