Updating citation information in README & documentation

[andyto1234]

I find the sunpy citation format and page very useful. Would suggest updating the Acknowledgments section in the documentation to include the 2023 paper. Just a suggestion though!

@ARTICLE{Weberg2023JOSS....8.4914W,
       author = {{Weberg}, Micah and {Warren}, Harry and {Crump}, Nicholas and {Barnes}, Will},
        title = "{EISPAC - The EIS Python Analysis Code}",
      journal = {The Journal of Open Source Software},
     keywords = {Python, astronomy, solar physics, spectroscopy},
         year = 2023,
        month = may,
       volume = {8},
       number = {85},
          eid = {4914},
        pages = {4914},
          doi = {10.21105/joss.04914},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2023JOSS....8.4914W},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}