Add doc preview (#3326)

Summary: Pull Request resolved: https://github.com/pytorch/audio/pull/3326

Reviewed By: hwangjeff

Differential Revision: D45760678

Pulled By: mthrok

fbshipit-source-id: 79b5d846c93516ca90c9700279124a9a04470242

.github/workflows/build_docs.yml

@@ -80,6 +80,7 @@ jobs:
         export BUILD_GALLERY=true
         (cd docs && make html)
 
+        cp -rf docs/build/html/* "${RUNNER_DOCS_DIR}"
         mv docs/build/html /artifacts/
 
   commit: