chore: update contributing.md adding details about a product oriented changelog

[fdefelici]

Description

This is a proposal to improve the contributing page about what change record can be included in the changelog or not.

Applicable issues

• fixes Improve Contributing page about changelog update #5939

Additional info (benefits, drawbacks, caveats)

Checklist

• Test coverage for new or modified code paths
• Changelog is updated
• Required documentation changes (e.g., docs/rpc/openapi.yaml and rpc-endpoints.md for v2 endpoints, event-dispatcher.md for new events)
• New clarity functions have corresponding PR in clarity-benchmarking repo
• New integration test(s) added to bitcoin-tests.yml

[wileyj]

lgtm

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.51%. Comparing base (c87ade3) to head (815a175).
Report is 36 commits behind head on develop.

❌ Your project status has failed because the head coverage (78.51%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

❗ There is a different number of reports uploaded between BASE (c87ade3) and HEAD (815a175). Click for more details.

HEAD has 10 uploads less than BASE

Flag	BASE (c87ade3)	HEAD (815a175)
	147	137

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #5925      +/-   ##
===========================================
- Coverage    83.70%   78.51%   -5.19%     
===========================================
  Files          521      521              
  Lines       382773   382815      +42     
  Branches       323      323              
===========================================
- Hits        320381   300566   -19815     
- Misses       62384    82241   +19857     
  Partials         8        8              

see 191 files with indirect coverage changes

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