added usage

README.md

@@ -5,4 +5,32 @@ Grafitti API for Minetest
 
 Code licensed as GPLv3 (see file LICENSE)  
 
-Screenshot:  
+Usage:  
+
+grafitti.register_grafitti(node_name, def)  
+-- node_name (eg. "default:stone")  
+-- def : {  
+--   image,  
+--   size = {x, y}, (optional, default: {1, 1})  
+--   center = {row, col}, (optional, default: {0, 0})  
+--   pointable (optional, default: false)  
+-- }  
+
+grafitti.set_palette_width(width)  
+-- Set GUI width for palette. If not set, default width is 8.  
+-- Use before palette build.  
+
+grafitti.palette_build(palette_name)  
+-- Place all previously registered grafitti into palette.  
+-- palette_name (eg. "mymod:nyancat_images")  
+
+grafitti.register_brush(brush_name, def)  
+-- Use after palette_build.
+-- brush_name (eg. "mymod:nyancat_brush")  
+-- def : {  
+--   palette (eg. "mymod:nyancat_images"),  
+--   description (optional),  
+--   inventory_image (optional),  
+--   wield_image (optional),  
+--   recipe (optional)  
+-- }