Fix the Towncrier philosophy link

[Jamim]

What do these changes do?

These changes fix a broken link to towncrier's philosophy.

Are there changes in behavior for the user?

Link from CHANGES/README.rst to towncrier's philosophy will be fixed.

Related issue number

Similar PR:

• Fix the Towncrier philosophy link frozenlist#574

Checklist

• I think the code is well written
• Documentation reflects the changes

Best regards!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cfdde40) 99.53% compared to head (4f2d714) 99.53%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #439   +/-   ##
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  Coverage   99.53%   99.53%           
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  Files           4        4           
  Lines         427      427           
  Branches       45       45           
=======================================
  Hits          425      425           
  Misses          1        1           
  Partials        1        1           

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