Some readme additions.

Especially regarding the different capabilities of the command line version vs. the Inkscape extension.

Author: cwalther

README.md

@@ -1,6 +1,9 @@
 # Cookie Cutter Sweeper
 
-Convert a black and white Cookie Cutter SVG shape into an STL file ready to be 3D printed.
+1. A command-line program that sweeps (extrudes) a 2D cross-section shape along the edge of a 2D shape, both given as black and white PNG files, and exports the resulting solid as a triangle mesh in STL format.
+2. An Inkscape extension using this for simple creation of 3D-printed cookie cutters from a black and white SVG shape.
+
+See [http://zurich.fablab.ch/2013/12/nicer-cookie-cutters/](http://zurich.fablab.ch/2013/12/nicer-cookie-cutters/) for a description of the algorithm and development history.
 
 ## Installing the Inkscape Extension
 
@@ -9,10 +12,12 @@ Convert a black and white Cookie Cutter SVG shape into an STL file ready to be 3
 
 ## Compiling the source code
 
-On the [releases page](https://github.com/cwalther/cookie-cutter-sweeper/releases) you can find binaries for most systems.
+On the [releases page](https://github.com/cwalther/cookie-cutter-sweeper/releases) you can find binaries for most systems as part of the Inkscape extension.
 
-If you want to compile yourself the c++ part of the plugin:
+If you want to compile yourself the c++ part of the plugin, install libpng development files in a place where `pkg-config` finds them and run
 
 ```sh
 make
 ```
+
+(or examine and adapt the makefile, it’s trivial).