install golangci-lint only if its not installed and update readme

[msherif1234]

Description

install golangci-lint only if its not installed

Dependencies

n/a

Checklist

If you are not familiar with our processes or don't know what to answer in the list below, let us know in a comment: the maintainers will take care of that.

• Is this PR backed with a JIRA ticket? If so, make sure it is written as a title prefix (in general, PRs affecting the NetObserv/Network Observability product should be backed with a JIRA ticket - especially if they bring user facing changes).
• Does this PR require product documentation?
  • If so, make sure the JIRA epic is labelled with "documentation" and provides a description relevant for doc writers, such as use cases or scenarios. Any required step to activate or configure the feature should be documented there, such as new CRD knobs.
• Does this PR require a product release notes entry?
  • If so, fill in "Release Note Text" in the JIRA.
• Is there anything else the QE team should know before testing? E.g: configuration changes, environment setup, etc.
  • If so, make sure it is described in the JIRA ticket.
• QE requirements (check 1 from the list):
  • Standard QE validation, with pre-merge tests unless stated otherwise.
  • Regression tests only (e.g. refactoring with no user-facing change).
  • No QE (e.g. trivial change with high reviewer's confidence, or per agreement with the QE team).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (ab18a4b) to head (f58b119).

Additional details and impacted files

@@          Coverage Diff          @@
##           main     #12    +/-   ##
=====================================
  Coverage      0   0.00%            
=====================================
  Files         0       5     +5     
  Lines         0     898   +898     
=====================================
- Misses        0     898   +898     

Flag	Coverage Δ
unittests	0.00% <ø> (?)

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[jpinsonneau]

Looks good, thanks @msherif1234 !