setup: prepare for pypi upload
add build/ and dist/ to gitignore
Test Plan
https://test.pypi.org/project/swh-loader-tar/
Migrated from D491 (view on Phabricator)
add build/ and dist/ to gitignore
https://test.pypi.org/project/swh-loader-tar/
Migrated from D491 (view on Phabricator)