docs: faq about character limit for network-based voices.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (b5a81fb) 99.28% compared to head (abf1a3a) 99.28%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #64 +/- ## ======================================= Coverage 99.28% 99.28% ======================================= Files 7 7 Lines 561 561 Branches 142 142 ======================================= Hits 557 557 Misses 4 4 ```

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