docs: Section on community use and contribution

[cadenmyers13]

Added a small section to index.rst that informs people that they can contribute to diffpy.cmi. @sbillinge Let me know your thoughts on the figure. The idea is that the community can fill in the empty/gray circles with their own modules.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.67%. Comparing base (d215a47) to head (203ca14).
⚠️ Report is 24 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #26   +/-   ##
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  Coverage   75.67%   75.67%           
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  Files           3        3           
  Lines          37       37           
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  Hits           28       28           
  Misses          9        9           

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[sbillinge]

I like the figure! We do actually have a SAS module, at least we need to get it going again but it is developed. We actually have an EXAFS module too but we never implemented it as we didn't think it was that useful. But for the purposes of the figure, adding a SAS module makes it look a bit more encouraging if people do want to contribute..... What do you think?

There is a paper describing the sas... https://journals.iucr.org/paper?S1600576713034055

[sbillinge]

This is looking really great! Please see my comments

[cadenmyers13]

What do you think?

@sbillinge Yeah I agree with adding these to the figure! I'll try to configure it and ping you when done!

[cadenmyers13]

@sbillinge How does this look?

[sbillinge]

love it!