add unitree dex3 (#4)

- [add] liscence of unitree dex3-1 (c141922edad40560a92c5277f7b2414fdd517c26)


Co-authored-by: pan <weison4ever@users.noreply.huggingface.co>

robots/unitree_hand/LICENSE

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+Copyright [2025] [HangZhou YuShu TECHNOLOGY CO.,LTD. ("Unitree Robotics")]
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+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.

robots/unitree_hand/README.md

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+Meshes and `unitree_dex3_left.urdf`,  `unitree_dex3_left.urdf`, `unitree_dex3_right.urdf` are copied from https://github.com/unitreerobotics/avp_teleoperate/tree/main/assets/unitree_hand.
+
+LICENSE is directly copied from https://github.com/unitreerobotics/avp_teleoperate/blob/main/LICENSE.