Add chromebrew instructions to ChromeOS flatpak setup

[saltedcoffii]

Currently, crostini, on some computers, breaks bubblewrap. Flatpaks can install but can't run. As an alternative method, please add instructions for installing flatpak on a chromebook using chromebrew, which does work.

Here are the step by step instructions:

1. Follow the instructions on the chromebrew README to install chromebrew. You will need to put your chromebook in developer mode.
2. Install flatpak with crew install flatpak.
3. Set up flathub flatpak remote-add --user --if-not-exists https://flathub.org/repo/flathub.flatpakrepo
4. Reload the chromebrew environment. source /usr/local/etc/profile
5. Shutdown and turn back on to set XDG environment variables. sudo reboot

Notes: Chromebrew doesn't support GUI launchers right now (coming soon!). For the time being, to run flatpakked software, run flatpak run com.domain.Project

[lucasgabmoreno]

Currently, crostini, on some computers, breaks bubblewrap. Flatpaks can install but can't run. As an alternative method, please add instructions for installing flatpak on a chromebook using chromebrew, which does work.

Here are the step by step instructions:

1. Follow the instructions on the chromebrew README to install chromebrew. You will need to put your chromebook in developer mode.
2. Install flatpak with crew install flatpak.
3. Set up flathub flatpak remote-add --user --if-not-exists https://flathub.org/repo/flathub.flatpakrepo
4. Reload the chromebrew environment. source /usr/local/etc/profile
5. Shutdown and turn back on to set XDG environment variables. sudo reboot

Flatpak is not working on Chromebrew: #11191
Can install flatpak and apps but can't make them run.

My steps to make install:

1. Install
   crew install flatpak OK
2. Repository
   flatpak --user remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo OK
3. Reboot
4. Install app
   flatpak install flathub org.gimp.GIMP OK
5. Run app
   flatpak run org.gimp.GIMP ERROR

[lucasgabmoreno]

Notes: Chromebrew doesn't support GUI launchers right now (coming soon!). For the time being, to run flatpakked software, run flatpak run com.domain.Project

There's a GUI launcher project: Crew launcher
But can't make it work #11190