docs: correct the API docs and readme before 0.18.0

[josephfusco]

A read with no timeout goes by each row's own expiry, and nine docblocks plus the README said it used the site's TTL; the suggested privacy policy text is the one change a site owner sees.

Related: #803

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.12%. Comparing base (7c91227) to head (6d710c4).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #820   +/-   ##
=========================================
  Coverage     97.12%   97.12%           
  Complexity      271      271           
=========================================
  Files            30       30           
  Lines          4375     4375           
=========================================
  Hits           4249     4249           
  Misses          126      126           

Flag	Coverage Δ
multisite	97.12% <100.00%> (ø)
phpunit	77.14% <100.00%> (ø)

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