Add toolkit link to API Reference index page

[dreadatour]

Follow-up for the #885

Could you add a link to to Overview page as well?

[cloudflare-workers-and-pages]

Deploying datachain-documentation with    Cloudflare Pages

Latest commit:	01b584b
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Preview URL:	https://a743e23a.datachain-documentation.pages.dev
Branch Preview URL:	https://docs-toolkit-index.datachain-documentation.pages.dev

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.75%. Comparing base (245204f) to head (01b584b).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #887   +/-   ##
=======================================
  Coverage   87.75%   87.75%           
=======================================
  Files         128      128           
  Lines       11456    11456           
  Branches     1544     1544           
=======================================
  Hits        10053    10053           
  Misses       1016     1016           
  Partials      387      387           

Flag	Coverage Δ
datachain	87.67% <ø> (ø)

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[yathomasi]

Thanks @dreadatour 🙏.