docs: add rebuild step to docs

README.rst

@@ -156,6 +156,7 @@ To contribute assets to Aspects:
 #. Run the command `tutor aspects check_superset_assets` to confirm there are no
    duplicate assets, which can happen when you rename an asset, and will cause import
    to fail. The command will automatically delete the older file if it finds a duplicate.
+#. Re-build your openedx-assets image with `tutor images build openedx-assets --no-cache`
 #. Check that everything imports correctly by running `tutor local do init -l aspects`
    and confirming there are no errors.
 #. Double check that your database password did not get exported before committing!