docs: use modern field API in 'boilerplate' section. (#1535)

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

* Adjust for review comment

* Tweak to second sentence.

* Apply suggestion from @hynek

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Co-authored-by: Hynek Schlawack <hs@ox.cx>

Author: carltongibson

docs/how-does-it-work.md

@@ -7,9 +7,8 @@
 *attrs* isn't the first library that aims to simplify class definition in Python.
 But its **declarative** approach combined with **no runtime overhead** lets it stand out.
 
-Once you apply the `@attrs.define` (or `@attr.s`) decorator to a class, *attrs* searches the class object for instances of `attr.ib`s.
-Internally they're a representation of the data passed into `attr.ib` along with a counter to preserve the order of the attributes.
-Alternatively, it's possible to define them using {doc}`types`.
+Once you apply the `@attrs.define` (or `@attr.s`) decorator to a class, *attrs* searches the class object for type hints and instances of `attrs.field`s.
+Internally `field`s are a representation of the data passed, along with a counter to preserve the order of the attributes.
 
 In order to ensure that subclassing works as you'd expect it to work, *attrs* also walks the class hierarchy and collects the attributes of all base classes.
 Please note that *attrs* does *not* call `super()` *ever*.