[DOC] Include strscan/lib

[naitoh]

#scan_integer was introduced at ruby/strscan#115
But it's not documented at https://docs.ruby-lang.org/en/master/StringScanner.html

See: ruby/strscan#176 (comment)

[kou]

Ah, we can't preview generated docs before merge a PR?

[hsbt]

Yes, it's hard to work only doc pull-request.

[kou]

OK. Can we try this in master? (Can we merge this?)

[naitoh]

Ah, we can't preview generated docs before merge a PR?

@kou

https://github.com/ruby/ruby/actions/runs/19725909577/job/56517250796
Artifact download URL: https://github.com/ruby/ruby/actions/runs/19725909577/artifacts/4693892901

[kou]

OK. Let's merge this.

[naitoh]

This has been reflected in the document. 🎉
https://docs.ruby-lang.org/en/master/StringScanner.html#method-i-scan_integer