Add Readme file

README.md

+# Extension "sodium_support"
+
+## What does it do?
+
+It adds support for the php crypto library [sodium](https://www.php.net/manual/de/book.sodium.php).
+This library provides several hash algorithms.
+
+This extension will use the argon2id password hashing ([RFC](https://tools.ietf.org/html/draft-irtf-cfrg-argon2-02))
+
+## Installation
+
+Install the extension via composer:
+
+`composer require fgtclb/sodium-support`
+
+## Dependencies
+
+This extension needs the PHP extension "sodium" to be installable.
+
+## Usage
+
+The extension automatically activates this hashing algorithm for FE and BE passwords.<br>
+You don't need to do anything.
+
+## Use another algorithm
+
+If you want to use another algorithm, please change the lines for FE and/or BE to the algorithm to use:
+
+```php
+$GLOBALS['TYPO3_CONF_VARS']['FE']['passwordHashing']['className'] = \Fgtclb\SodiumSupport\Crypto\PasswordHashing\SodiumPasswordHash::class;
+$GLOBALS['TYPO3_CONF_VARS']['BE']['passwordHashing']['className'] = \Fgtclb\SodiumSupport\Crypto\PasswordHashing\SodiumPasswordHash::class;
+```
+
+If you don't use this algorithm for none of them, you can easily remove this extension.
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