Add custom 404 page

[pgporada]

Currently a 404 shows us the default Netlify page rather than something with our personal flair.

[scottmakestech]

I can work on this.

[scottmakestech]

@pgporada What do you think of this?

https://deploy-preview-2130--letsencrypt.netlify.app/404

#2130

[mcpherrinm]

Looks great to me!

[scottmakestech]

Fixed by #2130