feat: huoyi M20 smooth/bridge training and stability docs

Current code snapshot: smooth/bridge task configs, smooth random terrain,
roll/pitch stability rewards, M20 URDF updates, eval profile and stability
training documentation.

.gitignore

@@ -0,0 +1,39 @@
+# Omniverse
+**/*.dmp
+**/.thumbs
+
+# Python
+.DS_Store
+**/*.egg-info/
+**/__pycache__/
+**/.pytest_cache/
+**/*.pyc
+**/*.pb
+
+# IDE
+**/.idea/
+**/.vscode/
+# Don't ignore the top-level .vscode directory as it is
+# used to configure VS Code settings
+!.vscode
+
+# Outputs
+**/runs/*
+**/logs/*
+**/recordings/*
+**/output/*
+**/outputs/*
+**/videos/*
+**/wandb/*
+**/.neptune/*
+docker/artifacts/
+*.tmp
+
+# Isaac-Sim packman
+_isaac_sim*
+_repo
+_build
+.lastformat
+
+
+**/usd/*