docs(README): fix URL in README.md

[WojciechKusa]

Description

fix link to Customization in README.md

Checklist

• Update the documentation for the changes

Expected behavior

Steps to Test This Pull Request

Check, that this URL is the correct one: https://commitizen-tools.github.io/commitizen/customization.html

Additional context

[woile]

I'd prefer to use https://commitizen-tools.github.io/commitizen/customization without the / if possible

[WojciechKusa]

That make sense, corrected

[codecov]

Codecov Report

Merging #404 (d595c61) into master (184c439) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #404   +/-   ##
=======================================
  Coverage   97.90%   97.90%           
=======================================
  Files          39       39           
  Lines        1381     1381           
=======================================
  Hits         1352     1352           
  Misses         29       29           

Flag	Coverage Δ
unittests	97.90% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
commitizen/__version__.py	100.00% <100.00%> (ø)

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[Lee-W]

Thanks for your fix!