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 88.93%. Comparing base (599e55c) to head (00dd95f).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #920      +/-   ##
==========================================
- Coverage   88.98%   88.93%   -0.05%     
==========================================
  Files          69       69              
  Lines        6754     6754              
==========================================
- Hits         6010     6007       -3     
- Misses        744      747       +3     

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