Add 404.html (#578)
Add 404.html (#578)

This 404.html comes from the minima project (https://github.com/jekyll/minima).
dennisdoomen/fluentassertions,vossad01/fluentassertions,jeroenpot/FluentAssertions,fluentassertions/fluentassertions,dennisdoomen/fluentassertions,fluentassertions/fluentassertions,jnyrup/fluentassertions,jnyrup/fluentassertions