Add doc about ArrayAccessTrait and ArrayIteratorTrait

[Tigrov]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	❌
Fixed issues

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.95%. Comparing base (5a2efc5) to head (3b53dc6).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #456   +/-   ##
=========================================
  Coverage     86.95%   86.95%           
  Complexity      667      667           
=========================================
  Files            40       40           
  Lines          1618     1618           
=========================================
  Hits           1407     1407           
  Misses          211      211           

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