update readme & add cdb metadata

.cdb.json

@@ -0,0 +1,16 @@
+{
+    "type": "MOD",
+    "title": "",
+    "name": "element_exchange",
+    "tags": [
+        "magic",
+        "technology"
+    ],
+    "license": "GPLv3",
+    "media_license": "GPLv3",
+    "short_description": "Exchange nodes into other nodes",
+    "dev_state": "ACTIVELY_DEVELOPED",
+    "repo": "https://github.com/enchant97/minetest_element_exchange.git",
+    "website": "https://github.com/enchant97/minetest_element_exchange",
+    "issue_tracker": "https://github.com/enchant97/minetest_element_exchange/issues"
+}

README.md

@@ -7,6 +7,15 @@ A [Minetest](https://www.minetest.net/) mod to exchange nodes into other nodes.
 
 ![In Game Screenshot](screenshot.png)
 
+## Features
+- Orb that holds energy
+- Collector that collects energy from the sun
+- Constructor that can convert one node into different node
+- Deconstructor that can extract energy from a node
+
+## Config
+You can change the default values in the minetest settings under `mods > element_exchange`.
+
 ## License
 Copyright (C) 2021 Leo Spratt