Added point about types to PR checklist

[sfc-gh-pmotacki]

Description

Added to PR checklist point: "Extend the types in index.d.ts file (if necessary)

Checklist

• Format code according to the existing code style (run npm run lint:check -- CHANGED_FILES and fix problems in changed code)
• Create tests which fail without the change (if possible)
• Make all tests (unit and integration) pass (npm run test:unit and npm run test:integration)
• Extend the README / documentation and ensure is properly displayed (if necessary)
• Provide JIRA issue id (if possible) or GitHub issue id in commit message

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.97%. Comparing base (c77f3d6) to head (8a5a5ca).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #920      +/-   ##
==========================================
+ Coverage   88.94%   88.97%   +0.03%     
==========================================
  Files          67       67              
  Lines        6459     6459              
==========================================
+ Hits         5745     5747       +2     
+ Misses        714      712       -2     

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