fix: remove deprecated fontSize heading limitation from readme (#497)

# Summary

Remove deprecated `fontSize` heading limitation from readme as it was
fixed here: #413

Author: kacperzolkiewski

README.md

@@ -268,7 +268,6 @@ See the [API Reference](docs/API_REFERENCE.md) for a detailed overview of all th
 ## Known limitations
 
 - Only one level of lists is supported. We currently do not support nested lists.
-- iOS headings can't have the same `fontSize` in their config as input's `fontSize`. Doing so results in incorrect headings behavior.
 
 ## Future Plans