Add MJCF model for Adam Lite robot

pndbotics_adam_lite/LICENSE

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+MIT License
+
+Copyright (c) 2023 pndrobotics
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

pndbotics_adam_lite/README.md

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+# PNDbotics Adam_lite Description (MJCF)
+
+Requires MuJoCo 2.3.3 or later.
+
+## Overview
+
+This package contains a simplified robot description (MJCF) of the
+[Adam_lite humanoid robot](https://www.pndbotics.com/humanoid) developed by [PNDbotics](https://www.pndbotics.com/about).
+
+<p float="left">
+  <img src="adam_lite.png" width="400">
+</p>
+
+## URDF → MJCF derivation steps
+
+1. Converted the DAE [mesh
+   files](https://github.com/RethinkRobotics/sawyer_robot/tree/master/sawyer_description/meshes)
+   to OBJ format using [Maya](https://www.autodesk.com/sg/products/maya/overview?term=1-YEAR&tab=subscription).
+2. Processed `.obj` files with [`obj2mjcf`](https://github.com/kevinzakka/obj2mjcf).
+3. Added `<mujoco> <compiler discardvisual="false"/> </mujoco>` to the
+   URDF`<robot>` clause in order to preserve visual geometries.
+4. Loaded the URDF into MuJoCo and saved a corresponding MJCF.
+5. Manually edited the MJCF to extract common properties into the `<default>` section.
+6. Manually designed collision geometries.
+7. Added `scene.xml` which includes the robot, with a textured groundplane, skybox, and haze.
+
+## License
+
+This model is released under an [MIT License](LICENSE).