Patch from Lubomír Bláha applied. Polished comments and PngExportDialog.

README.md

@@ -128,6 +128,7 @@ The author of the Silk icon set is Mark James.
         --post-process      Generated G-code will be processed with the supplied script;
                             call this more than once to process through multiple scripts.
         --export-svg        Export a SVG file containing slices instead of G-code.
+        --export-png        Export zipped PNG files containing slices instead of G-code.
         -m, --merge         If multiple files are supplied, they will be composed into a single
                             print rather than processed individually.
     
@@ -385,4 +386,4 @@ If you want to change a preset file, just do
 
 If you want to slice a file overriding an option contained in your preset file:
 
-    slic3r.pl --load config.ini --layer-height 0.25 file.stl
+    slic3r.pl --load config.ini --layer-height 0.25 file.stl