Update readme badges + code links

[tfiedlerdejanze]

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[sgerrand]

👋 @alan @telphan: Would you please trigger the test suite for @tfiedlerdejanze so that this change can be merged?

[tfiedlerdejanze]

Thanks for the nudge, which made me realize main is actually the active branch in Paginator. Unless there is a reason not to, i'd suggest the maintainers delete the master branch as it tends to be confusing to have both :)

[telphan]

@tfiedlerdejanze Good point, I removed master.