README.md standalone timezone info

[GeoDerp]

Looks like TZ defaults the system to UTC. However, I believe this only effects the Web_server diagrams (hence the note in README). Thanks goes to my Dad for finding this issue.

HA passes this variable with add-on. Therefore this issue should be standalone specific.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.54%. Comparing base (94c7421) to head (3b034ad).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #227   +/-   ##
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  Coverage   87.54%   87.54%           
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  Files           6        6           
  Lines        1710     1710           
=======================================
  Hits         1497     1497           
  Misses        213      213           

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