docs: update usage of single instance.

[x-cold]

Checklist

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

Affected core subsystem(s)

Description of change

[codecov]

Codecov Report

Merging #3 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master     #3   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           2      2           
  Lines          15     15           
=====================================
  Hits           15     15

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update be4178a...1b56f35. Read the comment docs.