Great little plugin

Excellent little plugin that will prove very useful. My use case for this is to discourage colleagues from uploading things they aren’t supposed to, such as:

• png, because almost certainly it’s a large file and may have transparency that we don’t need
• webp, because we still have plenty of customers with older safari versions that can’t use webp. We use cloudflare to deliver webp dynamically, so we want the site itself to have one version that is fully compatible as a fallback.

This plugin could be improved further by:

1. Tucking the Restrict Files admin menu item inside the media menu, and saying in the documentation where it is.
2. Adding a file size restriction.
3. Adding to the upload failure message to say what plugin has caused this limitation, so that a user has a clue what to do if they need an exception. “Sorry, you are not allowed to upload this file type, as it has been limited by the Restrict Files plugin.”