doc/toolbox: Add a usage section, and mention Arch Linux and Ubuntu as supported

[softwarefactory-project-zuul[bot]]

Build failed. https://softwarefactory-project.io/zuul/t/local/buildset/6097508f7a044af09c871834bb15a2b1

:heavy_check_mark: unit-test SUCCESS in 8m 15s :heavy_check_mark: unit-test-migration-path-for-coreos-toolbox SUCCESS in 3m 50s :heavy_check_mark: unit-test-restricted SUCCESS in 7m 37s :x: system-test-fedora-rawhide FAILURE in 35m 16s :heavy_check_mark: system-test-fedora-38 SUCCESS in 23m 48s :heavy_check_mark: system-test-fedora-37 SUCCESS in 23m 27s

[debarshiray]

There are still some test failures on Fedora Rawhide. For example:

fedora-rawhide | not ok 3 help: Run command 'help' in 145ms
fedora-rawhide | # (from function `assert_line' in file test/system/libs/bats-assert/src/assert.bash, line 479,
fedora-rawhide | #  in test file test/system/002-help.bats, line 45)
fedora-rawhide | #   `assert_line --index 0 --partial "toolbox(1)"' failed
fedora-rawhide | # /usr/bin/man
fedora-rawhide | #
fedora-rawhide | # -- line does not contain substring --
fedora-rawhide | # index     : 0
fedora-rawhide | # substring : toolbox(1)
fedora-rawhide | # line      : troff:<standard input>:33: warning: cannot select font 'C'
fedora-rawhide | # --

I believe these are because of changes in various other components in Fedora 39, which we need to track down one by one and work out a fix.

In the mean time, I am going to temporarily override these failures.

[softwarefactory-project-zuul[bot]]

Build failed. https://softwarefactory-project.io/zuul/t/local/buildset/487935c36e5c4454ad55bb8fbc6e9d7a

:heavy_check_mark: unit-test SUCCESS in 8m 54s :heavy_check_mark: unit-test-migration-path-for-coreos-toolbox SUCCESS in 4m 35s :heavy_check_mark: unit-test-restricted SUCCESS in 8m 05s :x: system-test-fedora-rawhide FAILURE in 33m 52s :heavy_check_mark: system-test-fedora-38 SUCCESS in 26m 31s :heavy_check_mark: system-test-fedora-37 SUCCESS in 24m 11s