Merge pull request #130 from AaronJan/patch-2

Add description for `docker-php-ext-install`

php/content.md

@@ -65,6 +65,27 @@ same commands to build and run:
 Where `src/` is the directory containing all your php code and `config/`
 contains your `php.ini` file.
 
+### How to install more PHP extensions
+
+We provide two convenient scripts named `docker-php-ext-configure` and `docker-php-ext-install`, you can use them to
+easily install PHP extension.
+
+For example, if you want to have a PHP-FPM image with `iconv`, `mcrypt` and `gd` 
+extensions, you can inheriting the base image that you like, and write your own 
+`Dockerfile` like this:
+
+    FROM php:5.5-fpm
+    # Install modules
+    RUN apt-get update && apt-get install -y \
+        libmcrypt-dev libpng12-dev libfreetype6-dev libjpeg62-turbo-dev \
+        && docker-php-ext-install iconv mcrypt \
+        && docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-gd-dir=/usr/include/ \
+        && docker-php-ext-install gd
+    CMD ["php-fpm"]
+
+Remember, you must install dependencies for your extensions manually. If an extension needs custom `configure` arguments,
+you can use the `docker-php-ext-configure` script like this example.
+
 ### Without a `Dockerfile`
 
 If you don't want to include a `Dockerfile` in your project, it is sufficient to