Adjust so it does not throw syntax errors and works for at least some
sampled `.fish` files.
Related #968, #258, #256
---
Sample `abook`:
```nushell
nu ❯ rm abook.nu -f; build-completion abook.fish abook.nu; open abook.nu
# Show usage
extern "abook" [
--add-email # Read email message from stdin and add the sender
--add-email-quiet # Same as --add-email. Without confirmation
--convert # Convert address book files
--informat # Input file format
--outformat # Output file format
--formats # Print available formats
...args
]
```
* Fix typo
* Add code fences
* Use `nushell` instead of `nu` code block language, so it renders
correctly on GitHub
* Use correct headline levels (only one instead of three top headlines)
* Add paragraph spacing where applicable
* Add trailing newline
A user in Discord recently tried to run the auto-generate script to
create completions from `<command> --help` and had issues. In examining
the scripts, I found that they used `build-string`, which was deprecated
and removed over 2 years ago. In order to prevent future confusion until
(and if) these files are updated, I'm moving them to a `needs-update`
directory in the repo.
Any other outdated files can be moved there as well.
