Clarify no-sandbox requirements

When running Linux container under Windows, no-sandbox is required or Chrome fails to launch. When running under Linux, this is not the case, per https://gitlab.com/aarongoldenthal/gitlab-pa11y-ci/pipelines/64533070.

Edited Jun 04, 2019 by Aaron Goldenthal

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information