Add 404 page
Add 404 page

This commit adds a basic 404 page so we are not using the default GitHub
Pages 404.

Signed-off-by: Matt Langbehn <be4a68432fbbc874fc2f26c6bc5da2cd4d88fc13@gmail.com>

BonnyCI/bonnyci.org,BonnyCI/bonnyci.org,BonnyCI/bonnyci.org,BonnyCI/bonnyci.org