docs: add yarn and pnpm installation

[snitin315]

• This is a bugfix
• This is a feature
• This is a code refactor
• This is a test update
• This is a docs update
• This is a metadata update

For Bugs and Features; did you add new tests?

No

Motivation / Use-Case

add yarn and pnpm installation.

Breaking Changes

No

Additional Info

No

[codecov]

Codecov Report

Merging #4257 (1a3fbaa) into master (c3b6690) will increase coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4257      +/-   ##
==========================================
+ Coverage   92.34%   92.47%   +0.12%     
==========================================
  Files          14       14              
  Lines        1541     1541              
  Branches      590      590              
==========================================
+ Hits         1423     1425       +2     
+ Misses        109      107       -2     
  Partials        9        9              

Impacted Files	Coverage Δ
lib/servers/WebsocketServer.js	94.87% <0.00%> (+5.12%)	⬆️

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