docs/ci: refresh README help; add lint; fix ShellCheck; guard /etc/inittab fallback

[VerdantE1]

For commit f3f166a

• Update README minimal help snippet to match current xsos -h output (v0.7.40)
• Document local lint commands in CONTRIB.md
• Add GitHub Actions workflow to run bash -n and shellcheck (errors only)

[VerdantE1]

For commit 2109939:

• Guard the /etc/inittab fallback with a readability check to avoid noisy errors when /etc/inittab is absent.
  Test:bash -n xsos && ./xsos >/dev/null

Why

• On modern Linux distributions (e.g., Ubuntu 22.04+, CentOS 8+, Debian 10+), the /etc/inittab file no longer exists because they use systemd instead of SysV init. This commit adds a simple guard: only read /etc/inittab if it exists and is readable. This eliminates the spurious error while preserving functionality on legacy systems that still have the file.

Changes

• Wrap /etc/inittab access with [ -f /etc/inittab ] && [ -r /etc/inittab ] check
• No change to output logic—just avoids attempting to read a non-existent file

[VerdantE1]

For commit 11cb227:

• Fix ShellCheck error-level findings (SC2068/SC2071) by quoting array expansions / using numeric comparisons, so CI passes.

[superjamie]

Thank you, this looks really good!

I'm currently on holiday. I will review this with intention to merge when I get back in Feb.

[VerdantE1]

Thank you, this looks really good!

I'm currently on holiday. I will review this with intention to merge when I get back in Feb.

Thanks! Enjoy your holiday 😊