[Fix] Add farseg's copyright

paddlers/custom_models/seg/models/farseg/farseg.py

@@ -11,6 +11,11 @@
 # 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 code is based on https://github.com/Z-Zheng/FarSeg
+Ths copyright of Z-Zheng/FarSeg is as follows:
+Apache License [see LICENSE for details]
+"""
 
 import math
 import paddle.nn as nn