docs: add pnpm example

[evenstensberg]

What kind of change does this PR introduce?

Docs

Did you add tests for your changes?
N/A
If relevant, did you update the documentation?
Yea
Summary
Adds pnpm line

Does this PR introduce a breaking change?

N/A

Other information
N/A

[codecov]

Codecov Report

Merging #3710 (c1fcd3a) into master (45979a0) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3710   +/-   ##
=======================================
  Coverage   91.38%   91.38%           
=======================================
  Files          22       22           
  Lines        1591     1591           
  Branches      448      448           
=======================================
  Hits         1454     1454           
  Misses        137      137           

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