At first, download public key poretsky.gpg that will be used for my signature verification and add it to the list of Apt keys by command:
$ sudo apt-key add poretsky.gpg
Or place it in /etc/apt/trusted.gpg.d directory that is the
preferred way in modern releases.
Then choose and download an accessibility.list file appropriate for
your distribution:
Place this file in /etc/apt/sources.list.d directory or simply copy
its content into your /etc/apt/sources.list file.
It is strongly recommended to make Apt prefer this repository to
prevent occasional installation of incompatible versions of some
packages from other sources. For this purpose download file
accessibility.pref and place it in
/etc/apt/preferences.d directory.