Update envelope-permits.md

Author: shannona

_pages/envelope-permits.md

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+## Overview
+
 Permits are cryptographic access control mechanisms that seal [Gordian Envelopes](/envelope/). They come in a variety of flavors, including symmetric keys, stretched passwords, public keys, SSKR shares, FROST multisig, and emerging quantum-resistant algorithms. Multiple permits can coexist in one Envelope, allowing different parties to access the same content in different ways. 
 
 ## Why Are Permits Important?