Do not recommend installing hub via Snap

It's just a bad system for this kind of CLI application.

Closes https://github.com/github/hub/issues/2565

README.md

@@ -43,7 +43,7 @@ Fedora Linux | [DNF](https://fedoraproject.org/wiki/DNF) | `sudo dnf install hub
 Arch Linux | [pacman](https://wiki.archlinux.org/index.php/pacman) | `sudo pacman -S hub`
 FreeBSD | [pkg(8)](http://man.freebsd.org/pkg/8) | `pkg install hub`
 Debian | [apt(8)](https://manpages.debian.org/buster/apt/apt.8.en.html) | `sudo apt install hub`
-Ubuntu | [Snap](https://snapcraft.io) | `sudo snap install hub --classic`
+Ubuntu | [Snap](https://snapcraft.io) | [We do not recommend installing the snap anymore.](https://github.com/github/hub/issues?q=is%3Aissue+snap)
 openSUSE | [Zypper](https://en.opensuse.org/SDB:Zypper_manual) | `sudo zypper install hub`
 Void Linux | [xbps](https://github.com/void-linux/xbps) | `sudo xbps-install -S hub`
 Gentoo | [Portage](https://wiki.gentoo.org/wiki/Portage) | `sudo emerge dev-vcs/hub`