Response to PyOpenSci review

[nwlandry]

This PR

• adds badges requested in Issue Add badges for repo status and python version #453.
• adds a bibtex citation in the README and the ReadTheDocs
• adds a more coherent explanation of what XGI is in the README.
• adds a page explaining "what are higher-order interactions?"
• adds an initial Gallery page of initializations
• updates the list of publications

Note that some of the links won't work until a new version is released.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.06% 🎉

Comparison is base (c5e8f0a) 91.81% compared to head (06ee1d0) 91.87%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #470      +/-   ##
==========================================
+ Coverage   91.81%   91.87%   +0.06%     
==========================================
  Files          60       60              
  Lines        4325     4371      +46     
==========================================
+ Hits         3971     4016      +45     
- Misses        354      355       +1     

see 2 files with indirect coverage changes

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