Add a template for custom 404 page (#5945)
Add a template for custom 404 page (#5945)

Merge pull request 5945
jekyll/jekyll,jaybe-jekyll/jekyll,rasa2011/rasa2011.github.io,yhironaka/yhironaka.github.io,tomjohnson1492/jekyll,chrisfinazzo/jekyll,fulldecent/jekyll,jekyll/jekyll,gencer/jekyll,tillgrallert/jekyll,chrisfinazzo/jekyll,fulldecent/jekyll,x-way/jekyll,alex-kovac/jekyll,Strangehill/jekyll,ryanshaw/jekyll,alex-kovac/jekyll,tillgrallert/jekyll,jaybe-jekyll/jekyll,x-way/jekyll,Strangehill/jekyll,tomjohnson1492/jekyll,ryanshaw/jekyll,tomjohnson1492/jekyll,alex-kovac/jekyll,ryanshaw/jekyll,gencer/jekyll,getandpost/jekyll.github.io,tillgrallert/jekyll,fulldecent/jekyll,tillgrallert/jekyll,Strangehill/jekyll,Strangehill/jekyll,jekyll/jekyll,tomjohnson1492/jekyll,alex-kovac/jekyll,getandpost/jekyll.github.io,Strangehill/jekyll,jaybe-jekyll/jekyll,rasa2011/rasa2011.github.io,x-way/jekyll,jekyll/jekyll,fulldecent/jekyll,alex-kovac/jekyll,tomjohnson1492/jekyll,rasa2011/rasa2011.github.io,getandpost/jekyll.github.io,gencer/jekyll,jaybe-jekyll/jekyll,x-way/jekyll,ryanshaw/jekyll,chrisfinazzo/jekyll,tillgrallert/jekyll,chrisfinazzo/jekyll,gencer/jekyll,gencer/jekyll