R1:10a84d66dbc9

Show a more tailored message when adding empty files

Summary: Fixes T6695. Tailor this message.

Test Plan: {F333305}

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T6695

Differential Revision: https://secure.phabricator.com/D12022