docs: add usage of startMode

[hyj1991]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

none

Description of change

add usage of startMode

[codecov]

Codecov Report

Base: 93.51% // Head: 93.51% // No change to project coverage 👍

Coverage data is based on head (0e17dae) compared to base (39715ae).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #102   +/-   ##
=======================================
  Coverage   93.51%   93.51%           
=======================================
  Files          12       12           
  Lines         787      787           
  Branches      119      119           
=======================================
  Hits          736      736           
  Misses         51       51           

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