Add note on normalization in charconv to docs

[mborland]

Closes: #787

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.9%. Comparing base (113de3d) to head (6e99976).
Report is 7 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop    #790     +/-   ##
=========================================
- Coverage     98.9%   98.9%   -0.0%     
=========================================
  Files          225     225             
  Lines        16940   16940             
  Branches      1806    1806             
=========================================
- Hits         16740   16739      -1     
- Misses         200     201      +1     

see 1 file with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 113de3d...6e99976. Read the comment docs.