Document that NUL (\0) strings is not supported

[w84thesun]

Description

This PR refs #169.

Readiness checklist

• I added tests for new functionality or bugfixes.
• I ran task all, and it passed.
• I added/updated comments for both exported and unexported top-level declarations (functions, types, etc).
• I checked comments rendering with task godocs.
• (for maintainers only) I set Reviewers, Assignee, Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[codecov]

Codecov Report

Merging #865 (6e5eff0) into main (6743b59) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #865   +/-   ##
=======================================
  Coverage   59.07%   59.07%           
=======================================
  Files         218      218           
  Lines        9855     9855           
=======================================
  Hits         5822     5822           
  Misses       3322     3322           
  Partials      711      711           

Impacted Files	Coverage Δ
internal/util/version/version.go	55.00% <0.00%> (-5.00%)	⬇️
internal/handlers/pg/pgdb/pool.go	57.88% <0.00%> (+0.57%)	⬆️

Flag	Coverage Δ
integration	61.51% <ø> (-0.04%)	⬇️
mongodb	18.76% <ø> (-0.04%)	⬇️
pg	61.44% <ø> (-0.04%)	⬇️
unit	24.68% <ø> (-0.06%)	⬇️

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[AlekSi]