cli onboard mixedreality (#12720)

* CLI onboard mixedreality

* brief params

* revert since fixed in modelerfour

Author: changlong-liu

specification/mixedreality/resource-manager/readme.az.md

@@ -0,0 +1,13 @@
+## AZ
+
+These settings apply only when `--az` is specified on the command line.
+
+``` yaml $(az)
+az:
+  extensions: mixedreality
+  package-name: azure-mgmt-mixedreality
+  namespace: azure.mgmt.mixedreality
+az-output-folder: $(azure-cli-extension-folder)/src/mixedreality
+python-sdk-output-folder: "$(az-output-folder)/azext_mixedreality/vendored_sdks/mixedreality"
+
+```

specification/mixedreality/resource-manager/readme.python.md

@@ -0,0 +1,4 @@
+## Python
+
+These settings apply only when `--python` is specified on the command line.
+