Improve error message from write-rustdoc-write-lines check

```
The following files are not formatted:
Error: - "../content/learn/book/storing-data/required-components.md"

Run write_rustdoc_hide_lines.sh to automatically fix these errors.
Error: Process completed with exit code 1.
```

The mention of `write_rustdoc_hide_lines.sh` is enough of a hint to go and find out what's happening here, but it would be a lot clearer if this error message included an explanation of what the check is actually for.

I'll have a go at coming up with a better message.

Locate the write_rustdoc_write_lines check and the referenced write_rustdoc_hide_lines.sh script. Read how the check reports the listed Markdown file and determine what explanation is missing from the message. Done means the failure output explains the check's purpose while retaining the affected file and automatic-fix guidance.

Written by the indexing model from the issue text.