chore: update toolkit-lib homepage to API Reference website

[iankhou]

Fixes the following—changes it to https://docs.aws.amazon.com/cdk/api/toolkit-lib/:

The homepage should be the API reference, not the Construct Library repo.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.31%. Comparing base (a560d1e) to head (64017d1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #922      +/-   ##
==========================================
- Coverage   83.44%   83.31%   -0.13%     
==========================================
  Files          71       71              
  Lines       10401    10401              
  Branches     1314     1311       -3     
==========================================
- Hits         8679     8666      -13     
- Misses       1684     1697      +13     
  Partials       38       38              

Flag	Coverage Δ
suite.unit	83.31% <ø> (-0.13%)	⬇️

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