chore: add the headings caveat to readme

Author: szydlovsky

README.md

@@ -812,6 +812,9 @@ interface MentionStyleProperties {
 - `fontSize` is the size of the heading's font, defaults to `32`/`24`/`20` for h1/h2/h3.
 - `bold` defines whether the heading should be bolded, defaults to `false`.
 
+> [!NOTE]
+> On iOS, the headings cannot have same `fontSize` as the component's `fontSize`. Doing so results in unexpected behavior.
+
 #### blockquote
 
 - `borderColor` defines the color of the rectangular border drawn to the left of blockquote text. Takes [color](https://reactnative.dev/docs/colors) value, defaults to `darkgray`.