Updated the base docs url to point to jbogard instead of headspringlabs

[jonsagara]

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Hi Jimmy,

The readme points to the docs at https://jbogard.github.io/bulk-writer/, but the links within the docs themselves still point to the old headspringlabs site (e.g., https://headspringlabs.github.io/bulk-writer/gettingstarted.html).

I'm not sure how the docs are generated, but hopefully this config change will result in the correct URLs in the docs.

Thanks,

Jon