Explain better the python_requires inheritance

@memsharded I'm thinking there should still be an update to the docs to explain that Conan inheritance is the same as regular Python inheritance, and maybe a small example to show that

_Originally posted by @cguldner in https://github.com/conan-io/docs/issues/1680#issuecomment-628622176_

Locate the documentation section for python_requires and read the existing inheritance guidance. Update it to explain that Conan inheritance follows regular Python inheritance and include a small example; done when both points are clearly documented.

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