docs: use modern field API in 'boilerplate' section.

[carltongibson]

Summary

Updates the text in the How does it work -> boilerplate section to use field rather than attr.ib.

Pull Request Check List

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  • Consider granting push permissions to the PR branch, so maintainers can fix minor issues themselves without pestering you.
• There's tests for all new and changed code.
• Changes or additions to public APIs are reflected in our type stubs (files ending in .pyi).
  • ...and used in the stub test file typing-examples/baseline.py or, if necessary, typing-examples/mypy.py.
  • If they've been added to attr/__init__.pyi, they've also been re-imported in attrs/__init__.pyi.
• The documentation has been updated.
  • New functions/classes have to be added to docs/api.rst by hand.
  • Changes to the signatures of @attr.s() and @attrs.define() have to be added by hand too.
  • Changed/added classes/methods/functions have appropriate versionadded, versionchanged, or deprecated directives.
    The next version is the second number in the current release + 1.
    The first number represents the current year.
    So if the current version on PyPI is 26.2.0, the next version is gonna be 26.3.0.
    If the next version is the first in the new year, it'll be 27.1.0.
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• Changes have news fragments in changelog.d.

Not sure if it needs a news item. I didn't add one (because likely not) but I didn't want to just tick it.

[hynek]

huh, that's really old and outdated since it ignores type annotations! I guess the sentence should go: searches the class object for type annotations and instances of `attrs.field`s.??

The second sentence is sadly still correct because I didn't dear to remove the counting logic because it would 100% break some code bases.

[carltongibson]

Like 3f891cf? (Can squash if you like)