Create README.md

Author: amculin

README.md

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+<h1 align="center"><b>Implementation of Vigenere Cipher in PHP</b></h1>
+<p align="center">
+  <img src="https://img.shields.io/packagist/dt/amculin/vigenere-cipher" alt="Packagist Download" />
+  <img src="https://img.shields.io/github/stars/amculin/php-vigenere-cipher" alt="GitHub Repo stars" />
+  <img src="https://img.shields.io/packagist/v/amculin/vigenere-cipher" alt="Packagist Version" />
+  <img src="https://img.shields.io/github/actions/workflow/status/amculin/php-vigenere-cipher/build.yml" alt="Passed Build Workflow" />
+  <img src="https://img.shields.io/badge/PHPStan-L_10-blue" alt="Passed PHPStan Level 10" />
+</p>
+
+Encrypt/decrypt string using Vigenere Cipher algorithm
+## Instalation
+```bash
+composer require amculin/vigenere-cipher
+```
+## How to use
+Encryption
+```php
+use amculin\cryptography\classic\VigenereCipher;
+
+$data = 'testtheencryptionprocess';
+$key = 'thisisthekey';
+
+//Basic mode only support lowercase alphabet
+//You can use alpha_numeric mode for wider supported characters (a-z, A-Z, 0-9)
+$encrypted = VigenereCipher::encrypt($data, $key, 'basic');
+
+echo "Plain text: {$data}\n";
+echo "Key: {$key}\n";
+echo "Cipher Text: {$encrypted}\n";
+```
+Output:
+```bash
+Plain text: testtheencryptionprocess
+Key: thisisthekey
+Cipher Text: mlalbzxlrmvwiaqgvhkvgowq
+```
+
+Decryption
+```php
+use amculin\cryptography\classic\VigenereCipher;
+
+$data = 'mlalbzxlrmvwiaqgvhkvgowq';
+$key = 'thisisthekey';
+$decrypted = VigenereCipher::decrypt($data, $key, 'basic');
+
+echo "Cipher text: {$data}\n";
+echo "Key: {$key}\n";
+echo "Plain Text: {$decrypted}\n";
+```
+Output:
+```bash
+Cipher Text: mlalbzxlrmvwiaqgvhkvgowq
+Key: thisisthekey
+Plain text: testtheencryptionprocess
+```
+
+## Features
+- [x] Support basic mode/lowercase alphabet only
+- [x] Support alpha-numeric mode (a-z, A-Z, 0-9)
+- [x] Unit test
+- [x] Comply PHPStan Level 10
+
+## Todos
+- [ ] Add ASCII mode to support file encryption/decryption
+- [ ] Add Base64 mode to support Base64 string