add short api to readme

README.md

@@ -1,5 +1,5 @@
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
-#Treasure
+# Minetest mod: Treasure
 
 Main repository:
 
@@ -11,17 +11,23 @@ https://gitlab.com/ademant/treasures.git
 
 https://github.com/ademant/treasures.git
 
-##Short description
+## Short description
 Outsource of treasure nodes from minerdream.
 
-##Longer description
-Five loot nodes are defined, which can be found in different depths. The possible drop items can be extended by other mods.
+## Longer description
+Five loot nodes are defined (treasures:treasure1 .. treasures:treasure5), which can be found in different depths. The possible drop items can be extended by other mods.
 
-#Authors of source code
+API:
 
-davieddoesminetest (MIT)
+- treasures.add_treasure(name,treasure_def) add a new node <name> similar to minetest.register_node
+- treasures.map_treasure(name,map_def) add the definition for map generation to treasure <name>
+- treasures.add_drop(name,drop_def) add to treasure <name> a new drop item (and optional rarety).
+
+# Authors of source code
+
+daviddoesminetest (MIT)
 
 ademant (MIT)
 
-#Authors of media (textures)
+# Authors of media (textures)