scripts: usability and readability improvements

[waldyrious]

I have tried to use some of the helper scripts at scripts/ and found them somewhat confusing and hard to reason about.
I decided to submit a few small improvements to make them slighly less mysterious to the uninitiated :)

• fix name and docs for get_pages_dirs()
• remove redundant split-rejoin operation
• print help when scripts are invoked without arguments

Checklist

• The PR is authored by me, or has been human-reviewed if it was created with AI or machine translation software.
• The PR title conforms to the recommended templates.