docs(readme): add cargo test instructions

[n0toose]

I came across a mysterious error that affected fs-test.

As I was experimenting with code affecting file reads and writes, I falsely assumed that the issue was isolated to this test in particular. I forgot that the rest of the tests would not get executed if the first one were to fail.

[n0toose]

A similar error appeared during the CI runs of #748, which caused some confirmation bias: I thought that only fs-test would fail on some environments, and not the integration tests as a whole. I'm trying to use that mistake to improve the docs for the "next person".

I can also modify the CI pipelines so as to use the --no-fail-fast flag after discussing and getting a positive signal on this PR.

[n0toose]

Related: #726 (comment)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.45%. Comparing base (f407069) to head (188a96e).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #760   +/-   ##
=======================================
  Coverage   67.45%   67.45%           
=======================================
  Files          20       20           
  Lines        2338     2338           
=======================================
  Hits         1577     1577           
  Misses        761      761           

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[jounathaen]

Hmm, honestly: I think this is rather verbose. The essence of this change is the --no-fail-fast flag, but this is nothing special to uhyve and also often not necessary. I think we should rather keep the README short. If there is a need for these kinds of information, we might consider adding a wiki.

If you think the --no-fail-fast information is of major importance, you can add a single sentence to the previous paragraph.

Please don't hesitate to re-open if you disagree.

[jounathaen]

You can also add that flag to the CI. That might be of value.