Reference the incubator repo in readme

[gadomski]

Description

Adds a note to the readme re: the incubator repo.

Checklist

• Documentation, including doctests
• Git history is linear
• Commit messages are descriptive
• (optional) Git commit messages follow conventional commits
• Code is formatted (cargo fmt)
• cargo test

[codecov-commenter]

Codecov Report

Merging #66 (075ebfe) into main (514a155) will decrease coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #66      +/-   ##
==========================================
- Coverage   64.91%   64.84%   -0.08%     
==========================================
  Files          17       17              
  Lines        1374     1374              
  Branches      349      351       +2     
==========================================
- Hits          892      891       -1     
  Misses        183      183              
- Partials      299      300       +1     

Impacted Files	Coverage Δ
src/href.rs	70.84% <0.00%> (-0.34%)	⬇️

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