Add docs for Linkedin OpenID Connect

[noxan]

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• I have added documentation to https://github.com/python-social-auth/social-docs

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[noxan]

@nijel here finally the docs for linked openid connect, was on vacations for a while.

also short note here: linkedin openid connect does not work without python-social-auth/social-core#852, so would be amazing to have it released soon - thanks for all your great work :)

[nijel]

Thanks, looks good: https://python-social-auth--191.org.readthedocs.build/en/191/backends/linkedin.html