add notes on scope to the README

Author: jcupitt

README.md

@@ -1,17 +1,18 @@
 # High-level PHP binding for libvips 
 
-A high-level interface to the libvips image processing library. This
-module builds upon the `vips` extension, see:
-
-https://github.com/jcupitt/php-vips-ext
-
-You'll need to install that first. It's tested on Linux, OS X should work,
-Windows would need some work, but should be possible.  
+`php-vips` is a binding for [libvips](https://github.com/jcupitt/libvips), in
+line with [ruby-vips](https://github.com/jcupitt/ruby-vips),
+[pyvips](https://github.com/jcupitt/libvips/tree/master/python), the [libvips
+C++ API](https://github.com/jcupitt/libvips/tree/master/cplusplus) and the
+[libvips C API](https://github.com/jcupitt/libvips/tree/master/libvips).  
+It aims to be small and simple, and to provide a stable, well-documented
+platform that conforms to [PHP standards
+recommendations](http://www.php-fig.org/psr/).
 
 libvips is fast and it can work without needing to have the 
 entire image loaded into memory. Programs that use libvips don't
 manipulate images directly, instead they create pipelines of image processing
-operations starting from a source image. When the end of the pipe is connected
+operations starting from a source image. When the pipe is connected
 to a destination, the whole pipeline executes at once, streaming the image
 in parallel from source to destination in a set of small fragments. 
 
@@ -24,11 +25,27 @@ There's a handy blog post explaining [how libvips opens
 files](http://libvips.blogspot.co.uk/2012/06/how-libvips-opens-file.html)
 which gives some more background.
 
+Extra functionality, such as an image thumbnailer, for example, is 
+implemented in repositories which build on this one, and not incorporated
+directly in this code (though see `examples/`).
+As much of the binding as possible is auto-generated. This reduces
+maintenance effort, increases reliability, and makes it possible to
+reuse core libvips documentation.
+
+This
+module builds upon the `vips` binary extension, see:
+
+https://github.com/jcupitt/php-vips-ext
+
+You'll need to install that first. It's tested on Linux; OS X should work;
+Windows would need some work, but should be possible.  
+
 ### Example
 
 ```php
 #!/usr/bin/env php
 <?php
+require __DIR__ . '/vendor/autoload.php';
 use Jcupitt\Vips;
 
 $image = Vips\Image::newFromFile($argv[1]);