[doc, Q1'25-CQH] synthetic benchmarks documentation updates

[ssavenko-near]

Clarifies usage and some gotchas I encountered while getting acquainted with the tool

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.45%. Comparing base (5581f65) to head (911433a).
Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12812      +/-   ##
==========================================
- Coverage   70.46%   70.45%   -0.01%     
==========================================
  Files         847      847              
  Lines      175138   175001     -137     
  Branches   175138   175001     -137     
==========================================
- Hits       123416   123304     -112     
+ Misses      46463    46441      -22     
+ Partials     5259     5256       -3     

Flag	Coverage Δ
backward-compatibility	0.16% <ø> (+<0.01%)	⬆️
db-migration	0.16% <ø> (+<0.01%)	⬆️
genesis-check	1.41% <ø> (+<0.01%)	⬆️
linux	70.06% <ø> (+0.02%)	⬆️
linux-nightly	70.10% <ø> (+<0.01%)	⬆️
pytests	1.70% <ø> (+<0.01%)	⬆️
sanity-checks	1.52% <ø> (+0.01%)	⬆️
unittests	70.29% <ø> (-0.01%)	⬇️
upgradability	0.20% <ø> (+<0.01%)	⬆️

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