Fix typo in bash completion, add help completion

[mabelzhang]

🦟 Bug fix

2 fixes before further changes to the file while working on #1. Original code #77.

• COMPWORDS is a typo
• ign help was not in tab completion. Now you can type ign <tab> and get help as a possible completion.

Summary

Test with this:

. etc/ign.bash_completion.sh

# `help` should be listed as an available command after the PR
ign <tab>

# `help` should be auto completed
ign h<tab>

Checklist

• [x] Signed all commits for DCO
• [ ] Added tests
• [ ] Updated documentation (as needed)
• [ ] Updated migration guide (as needed)
• [ ] codecheck passed (See contributing)
• [ ] All tests passed (See test coverage)
• [ ] While waiting for a review on your PR, please help review another open pull request to support the maintainers

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