PEP 696: Update pep-0696.rst to make the explanations of Abstract and Motivation section clearer

[hyperkai]

I made the explanations of Abstract and Motivation section clearer.

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📚 Documentation preview 📚: https://pep-previews--4722.org.readthedocs.build/

[skirpichev]

This PEP is historical document, please see Important note:

This PEP is a historical document: see Defaults for Type Parameters and Type parameter lists for up-to-date specs and documentation. Canonical typing specs are maintained at the typing specs site; runtime typing behaviour is described in the CPython documentation.

See the typing specification update process for how to propose changes to the typing spec.