Improve text of message attached to uploaded image

Requested by Commons admins User:INeverCry and User:Ellin_Beltz
by way of Philippe

See https://commons.wikimedia.org/wiki/Commons:Deletion_requests/Files_uploaded_by_Selenium_user

I also updated the information at https://commons.wikimedia.org/wiki/User:Selenium_user

Change-Id: I67435f28b685ac0472a25fb0cb6b7cdd096e03ec