Add GTK 4.6 Warning to README

README.md

@@ -9,6 +9,12 @@ install on Ubuntu. If you're looking for the Ghostty source code, see
 
 ## How To Install Ghostty on Ubuntu
 
+> ![WARNING]
+> A recent GTK is required for Ghostty to work with Nvidia (GL) drivers under
+> x11. **Ubuntu 22.04 LTS has GTK 4.6 which is not new enough.** (See the
+> [note](https://ghostty.org/docs/install/build#debian-and-ubuntu) in the
+> Ghostty docs.)
+
 1. Download the most recent .deb package for your Ubuntu version from the
    [Releases](https://github.com/mkasberg/ghostty-ubuntu/releases) page.
 2. Install the downloaded .deb package by running `sudo dpkg -i