🍇 add favicon to documentation pages too

[joeskeen]

I realized after #99 was merged that there still was no favicon in the docs such as https://www.emojicode.org/docs/guides/compile-and-run.html, although it does properly show up on the home page https://www.emojicode.org/. I added the favicon to the other main HTML file so that it should show up everywhere on the site.