[docs] introduction chapter

doc/00-intro.md

@@ -0,0 +1,65 @@
+# Introduction
+
+Composer is a tool for dependency management in PHP. It allows you to declare
+the dependencies of your project and will install these dependencies for you.
+
+## Dependency management
+
+One important distinction to make is that composer is not a package manager. It
+deals with packages, but it manages them on a per-project basis. By default it
+will never install anything globally. Thus, it is a dependency manager.
+
+This idea is not new by any means. Composer is strongly inspired by
+node's [npm](http://npmjs.org/) and ruby's [bundler](http://gembundler.com/).
+But there has not been such a tool for PHP so far.
+
+The problem that composer solves is the following. You have a project that
+depends on a number of libraries. Some of libraries have dependencies of their
+own. You declare the things you depend on. Composer will then go ahead and
+find out which versions of which packages need to be installed, and install
+them.
+
+## Declaring dependencies
+
+Let's say you are creating a project, and you need a library that does logging.
+You decide to use [monolog](https://github.com/Seldaek/monolog). In order to
+add it to your project, all you need to do is create a `composer.json` file
+which describes the project's dependencies.
+
+```json
+{
+    "require": {
+        "monolog/monolog": "1.0.2"
+    }
+}
+```
+
+We are simply stating that our project requires the `monolog/monolog` package,
+version `1.0.2`.
+
+## Installation
+
+To actually get it, we need to do two things. The first one is installing
+composer:
+
+    $ curl -s http://getcomposer.org/installer | php
+
+This will just check a few PHP settings and then download `composer.phar` to
+your working directory. This is the composer binary.
+
+After that we run the command for installing all dependencies:
+
+    $ php composer.phar install
+
+This will download monolog and dump it into `vendor/monolog/monolog`.
+
+## Autoloading
+
+After this you can just add the following line to your bootstrap code to get
+autoloading:
+
+```php
+require 'vendor/.composer/autoload.php';
+```
+
+That's all it takes to have a basic setup.