Update README.md

Author: DivineOmega

README.md

@@ -3,8 +3,20 @@
 [![Build Status](https://travis-ci.com/DivineOmega/php-ssh-connection.svg?branch=master)](https://travis-ci.com/DivineOmega/php-ssh-connection)
 [![Coverage Status](https://coveralls.io/repos/github/DivineOmega/php-ssh-connection/badge.svg?branch=master)](https://coveralls.io/github/DivineOmega/php-ssh-connection?branch=master)
 
+The PHP SSH Connection package provides an elegant syntax to connect to SSH servers and execute commands. It supports both password and public-private keypair authentication, and can easily capture command output and errors.
+
 ## Installation
 
+First, you may need to install the PHP SSH2 extension. In Ubuntu and other Debian-based systems, you can install this extension by running the following command.
+
+```bash
+sudo apt install php-ssh2
+```
+
+For other operating systems, see the [PHP SSH2 extension documentation](https://www.php.net/manual/en/book.ssh2.php).
+
+You can then run the following Composer command to install the PHP SSH Connection package.
+
 ```bash
 composer require divineomega/php-ssh-connection
 ```
@@ -24,4 +36,4 @@ $command = $connection->run('echo "Hello world!"');
 
 $command->getOutput();  // 'Hello World'
 $command->getError();   // ''
-```
+```