docs: adding a documentation

docs/adapters.md

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+# Adapters
+
+## APCu Adapter
+
+The APCu adapter requires a APCu extension.
+
+```php
+$pool = new \Charon\Cache\Adapter\APCu\APCuAdapter(
+
+);
+```
+
+## Array Adapter
+
+The Array adapter is useful for testing purposes, as its data stored in memory.
+
+```php
+$pool = new \Charon\Cache\Adapter\Array\ArrayAdapter(
+
+);
+```

docs/index.md

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+# charon-cache
+
+## Installation
+
+```bash
+composer require charonlab/charon-cache
+```
+
+## Support
+
+- Sources available at [github](https://github.com/charonlab/charon-cache).
+- Report a bug [here](https://github.com/charonlab/charon-cache/issues)

docs/usage.md

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+# Usage
+
+This following example shows basic usage of the cache:
+```php
+
+$value = $cache->get('foobar', function (\Charon\Cache\CacheItemPool $item): string {
+    // The callback will be called only when the cache miss.
+    return 'cachepool';
+});
+
+// Output: 'cachepool'
+echo $value;
+
+// Clears the cache value.
+$cache->delete('foobar');
+```