It adds 3 Advancements:
1. find a mushroom biome
2. find a mesa biome
3. find a modiefied jungle edge biome
For each, you get a reward and for the jungle edge, you even get some of the most illegal items ever!

How to download:

When you click on the link to download, it will redirect you to a website.
Wait 6 seconds, and then click on the top right corner 'skip'
Ignore everything else on the page.
You will then be redirected to the download link, click on download, and you're done!