README updated

README.md

@@ -1,2 +1,38 @@
 # cairo_jpg
-Reading and writing JPEG files from/to Cairo surfaces.
+
+## Introduction
+
+This is an implementation of functions to import and export Cairo surfaces from
+and to JPEG files. It uses the same function prototypes as Cairo's [PNG
+support](http://www.cairographics.org/manual/cairo-PNG-Support.html).
+
+## Description
+
+The implementation is done on top of the Cairo API. It does not access
+Cairo-internal functions.
+For compression and decompression [libjpeg](http://libjpeg.sourceforge.net/) is
+used.
+
+The following prototypes are implemented. Their functionallity is equal to the
+PNG functions of Cairo with the advance that there are memory-buffer-based
+functions as well.
+
+```C
+cairo_status_t cairo_image_surface_write_to_jpeg_mem(cairo_surface_t *sfc, unsigned char **data, size_t *len, int quality);
+cairo_status_t cairo_image_surface_write_to_jpeg_stream(cairo_surface_t *sfc, cairo_write_func_t write_func, void *closure, int quality);
+cairo_status_t cairo_image_surface_write_to_jpeg(cairo_surface_t *sfc, const char *filename, int quality);
+cairo_surface_t *cairo_image_surface_create_from_jpeg_mem(void *data, size_t len);
+cairo_surface_t *cairo_image_surface_create_from_jpeg_stream(cairo_read_func_t read_func, void *closure);
+cairo_surface_t *cairo_image_surface_create_from_jpeg(const char *filename);
+```
+
+To compile this code you need to have installed the packages libcairo2-dev
+and libjpeg-dev. Compile with the following command to create an object file
+linkable to your code:
+```Shell
+gcc -Wall -c `pkg-config cairo libjpeg --cflags --libs` cairo_jpg.c
+```
+
+Please have a look at the comments within the source files for further details.
+Don't hesitate to contact me at [bf@abenteuerland.at](mailto:bf@abenteuerland.at).
+