Update docs to support go-github `DisableRateLimitCheck`

[stevehipwell]

The latest version of go-github has added a DisableRateLimitCheck field to the client to support offloading rate limit checks to another library such as this without having to pass a context flag in evry request.

[github-actions]

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[gofri]

@stevehipwell thanks!
I really appreciate your contribution (both in go-github and with this issue).
I'll update the examples and docs to reflect that. Feel free to open a PR if you'd like :)

p.s. I'm just curious; did you add it there for this purpose? i.e., did you find the behavior of go-github before this fix conflicting with the middleware?

[stevehipwell]

@gofri I want to use your middleware in a couple of projects and I wanted a clean separation that would be easy to manage. The previous rate limiting code in go-github looked to have side effects even when disabled and the context propagation pattern made it tricky to manage globally (and to easily test the different implementations).