Make benchmarks easier to run

[gadomski]

Related Issue(s): None

Description:
Uses the --benchmark-skip option in pytest.ini to skip benchmarks, instead of an explicit skip decorator. Includes a section in the README on how to run benchmarks.

@matthewhanson I couldn't figure out how to run the benchmarks w/o deleting the skip line -- if you had a way to do it from the command line, I'm happy to revert this change and just document the way you were running them.

PR Checklist:

• Code is formatted
• Tests pass
• Changes are added to the CHANGELOG

[codecov-commenter]

Codecov Report

Merging #168 (6e4bb7f) into main (fbcadb8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #168   +/-   ##
=======================================
  Coverage   83.93%   83.93%           
=======================================
  Files           9        9           
  Lines         660      660           
=======================================
  Hits          554      554           
  Misses        106      106           

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[gadomski]

@philvarner can you review this just for the CHANGELOG fixes? I think auto-merging was putting changelog entries into a weird place, so I fixed things up. Check v0.3.5...benchmark for the diff from v0.3.5 to this branch.

[philvarner]

@philvarner can you review this just for the CHANGELOG fixes? I think auto-merging was putting changelog entries into a weird place, so I fixed things up. Check v0.3.5...benchmark for the diff from v0.3.5 to this branch.

Looks good -- those got very messed up