README.md: Add badges.

Author: samuel-lucas6

README.md

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+[![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](https://github.com/samuel-lucas6/DoubleSec/blob/main/LICENSE)
+[![CodeQL](https://github.com/samuel-lucas6/DoubleSec/actions/workflows/codeql-analysis.yml/badge.svg)](https://github.com/samuel-lucas6/DoubleSec/actions)
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 # DoubleSec
 DoubleSec is a simple, double-paranoid encryption library inspired by [TripleSec](https://keybase.io/triplesec/). It encrypts data with XChaCha20 and AES-CTR to account for a future compromise of one of these ciphers.