Update the README with common options and commands

[camembera]

.. and at least mention the CHAIN_SPEC variable.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 60.91%. Comparing base (1027373) to head (d90fd54). :warning: Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2621   +/-   ##
=======================================
  Coverage   60.91%   60.91%           
=======================================
  Files         358      358           
  Lines       16864    16864           
=======================================
  Hits        10272    10272           
  Misses       5796     5796           
  Partials      796      796           

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• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Manikbff]

marge me