MRG: update plugin documentation for users

[ctb]

• Fixes plugin version command #3271 by adding "versions" to sourmash info -v info.
• Starts to tackle add plugin information to docs #2870

Related issues:

• upgrade plugin documentation #2695

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.75%. Comparing base (9fc7700) to head (ea22c6d).
Report is 63 commits behind head on latest.

Additional details and impacted files

@@           Coverage Diff           @@
##           latest    #3286   +/-   ##
=======================================
  Coverage   86.75%   86.75%           
=======================================
  Files         137      137           
  Lines       15920    15920           
  Branches     2728     2728           
=======================================
  Hits        13812    13812           
  Misses       1799     1799           
  Partials      309      309           

Flag	Coverage Δ
hypothesis-py	25.40% <ø> (ø)
python	92.37% <ø> (ø)
rust	62.67% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[ctb]

Ready for review & merge @sourmash-bio/devs