Update "Downstream" part of readme

[aguschin]

Add link to the workflow in gto-example, GTO GH Action, and actualize examples for check-ref.

[codecov-commenter]

Codecov Report

Base: 80.91% // Head: 81.88% // Increases project coverage by +0.97% 🎉

Coverage data is based on head (4784b90) compared to base (691ca4b).
Patch coverage: 92.42% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #263      +/-   ##
==========================================
+ Coverage   80.91%   81.88%   +0.97%     
==========================================
  Files          16       16              
  Lines        1886     1905      +19     
==========================================
+ Hits         1526     1560      +34     
+ Misses        360      345      -15     

Impacted Files	Coverage Δ
gto/config.py	95.78% <ø> (ø)
gto/cli.py	70.43% <86.20%> (+0.86%)	⬆️
gto/registry.py	74.89% <88.88%> (+1.61%)	⬆️
gto/api.py	90.98% <100.00%> (+12.72%)	⬆️
gto/base.py	85.83% <100.00%> (+0.44%)	⬆️
gto/constants.py	100.00% <100.00%> (ø)
gto/_version.py	36.36% <0.00%> (-45.46%)	⬇️
... and 1 more

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