Improve measurement details in README for phpunit 10+

[mvorisek]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.77%. Comparing base (9740a48) to head (deece2f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #452   +/-   ##
=========================================
  Coverage     58.77%   58.77%           
  Complexity      135      135           
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  Files            33       33           
  Lines           701      701           
=========================================
  Hits            412      412           
  Misses          289      289           

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[mvorisek]

Firstly, thank you for merging the #380 PR!

I did my best to improve the README for new users, especially to stress:

• the before/after class test methods are measured only when phpunit process isolation is enabled
• remove the notes telling the durations might vary on a tests order, this is not true

[mvorisek]

@localheinz is this PR welcomed?

[mvorisek]

@localheinz are you interested in this README improvement or should I close this PR?

[localheinz]

Apologies for the delay, I’m busy with closed-source projects at the moment. Will take a look later in the year!

[localheinz]

Thank you, @mvorisek!