Add a note about 404 pages on the deploying page
Add a note about 404 pages on the deploying page

Fixes #732

waylan/mkdocs,mkdocs/mkdocs,d0ugal/mkdocs,jimporter/mkdocs,d0ugal/mkdocs,lukfor/mkdocs,lukfor/mkdocs,d0ugal/mkdocs,jimporter/mkdocs,mkdocs/mkdocs,waylan/mkdocs,lukfor/mkdocs,jimporter/mkdocs,waylan/mkdocs,mkdocs/mkdocs