Add Sponsors Button to GitHub Repo
While discussion on other support avenues are still ongoing, I think it would still be beneficial to add the a Sponsors Button to the repo that points to https://pandas.pydata.org/donate.html

Note: https://www.flipcause.com/secure/cause_pdetails/MzA3OA== is the direct page to donate but this link doesn't appear as "donate friendly" IMO

Let me know if there's a better link to reference 

Reference to the Support Button on Numpy's page: https://github.com/numpy/numpy/pull/13700
