Update project page with Drupal 9 information

Problem/Motivation

The project page is missing information about Drupal 9.

Proposed resolution

Per tweet:

https://twitter.com/DropIsMoving/status/1130868996771844096

please update the project page to point to the two D9 issues being worked on:

#3100388: Drupal 9 compatibility
#3091388: Fix deprecations including jQuery UI dependency and info.yml update

Remaining tasks

Edit project page

User interface changes

N/A

API changes

N/A

Data model changes

N/A

Release notes snippet

N/A