[ISSUE-216] Add CHANGELOG for v6.0.0

[jama5262]

What does this PR do?

Add CHANGELOG for v6.0.0

Issue Reference

Fixes #216

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Maintenance change (non-breaking change such as upgrading a dependency, refactoring, or making a lint fix)
• Documentation update
• Breaking change (a fix or feature that would cause existing functionality to change)

Screenshots

If applicable, add screenshots to help explain your problem.

Checklist

• Wrote additional tests, if needed
• All tests have passed
• I have updated the documentation accordingly, if needed.

Additional Information

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (c907281) 96.30% compared to head (3fbfbb3) 96.30%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #217   +/-   ##
=======================================
  Coverage   96.30%   96.30%           
=======================================
  Files          34       34           
  Lines        1544     1544           
=======================================
  Hits         1487     1487           
  Misses         57       57           

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