Add installation instructions for different methods

doc/1_Installation.markdown

@@ -0,0 +1,48 @@
+Installation
+============
+
+There are multiple ways to include the PHP parser into your project:
+
+Installing from the Zip- or Tarball
+-----------------------------------
+
+Download the latest version from [the download page][2], unpack it and move the files somewhere into your project.
+
+Installing via Composer
+-----------------------
+
+Create a `composer.json` file in your project root and use it to define your dependencies:
+
+    {
+        "require": {
+            "nikic/php-parser": "0.9.1"
+        }
+    }
+
+Then install Composer in your project (or [download the composer.phar][1] directly):
+
+    curl -s http://getcomposer.org/installer | php
+
+And finally ask Composer to install the dependencies:
+
+    php composer.phar install
+
+Installing as a PEAR package
+----------------------------
+
+Run the following two commands:
+
+    pear channel-discover nikic.github.com/pear
+    pear install channel://nikic.github.com/pear/PHPParser-0.9.1
+
+Installing as a Git Submodule
+-----------------------------
+
+Run the following command to install the parser into the `vendor/PHP-Parser` folder:
+
+    git submodule add git://github.com/nikic/PHP-Parser.git vendor/PHP-Parser
+
+
+
+ [1]: http://getcomposer.org/composer.phar
+ [2]: https://github.com/nikic/PHP-Parser/tags