Add OpenUSD MuJoCo setup scripts and wrapper examples

docs/openusd/README.md

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+# MuJoCo + OpenUSD Setup Notes
+
+This documents the current OpenUSD-enabled MuJoCo setup used for USD asset/environment import testing.
+
+## Current Purpose
+
+This work is focused on the OpenUSD -> MuJoCo import path.
+
+It is not policy training yet. The goal is to make MuJoCo able to load and visualize USD-based assets/environments so they can later be tested with Seahorse, RoboJudo, and ProtoMotion workflows.
+
+## Build Flow
+
+1. Clone stable MuJoCo.
+2. Build OpenUSD using MuJoCo's helper:
+
+   `cmake/third_party_deps/openusd`
+
+3. Configure MuJoCo with OpenUSD enabled:
+
+   `-DMUJOCO_WITH_USD=True`
+
+4. Build MuJoCo.
+5. Verify that `build/bin/simulate` exists.
+6. Launch MuJoCo using the runtime helper script:
+
+   `scripts/openusd/run_mujoco_usd.sh`
+
+## Runtime Helper
+
+The runtime helper script sets the paths needed for MuJoCo to find the USD decoder plugin and OpenUSD libraries.
+
+It handles:
+
+- `libusd_decoder_plugin.so`
+- `LD_LIBRARY_PATH`
+- `PXR_PLUGINPATH_NAME`
+- WSL graphics settings using `llvmpipe`
+
+## XML Wrapper Testing
+
+USD assets are loaded through MJCF XML wrapper files.
+
+The important MJCF line is:
+
+    <model name="asset_name" file="/path/to/file.usd" content_type="text/usd"/>
+
+The wrapper gives MuJoCo simulation context such as:
+
+- asset path
+- worldbody
+- lighting
+- floor
+- attach point
+
+## Current Limitation
+
+This does not automatically convert a full Isaac Sim task into a MuJoCo training environment.
+
+Physics, contacts, joints, actuators, rewards, and policy training still need separate validation.