docs: add `rtl` example

[zaaakher]

This PR simply adds a RTL example.

Note: This PR should wait on https://github.com/TypeCellOS/BlockNote/pull/922, If the team decides to accept the dir prop to BlockNoteView then I will update this PR to include passing a dir='rtl'

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[matthewlipski]

Looks good! Think it just depends on @YousefED's feedback on #922