Updated JSON API (markdown)

JSON-API.md

@@ -1,6 +1,20 @@
 Check back soon! This documentation is scheduled to be completed before the 3rd of April 2019
 
-Sample JSON API response (v0.8.4)
+Starting from version 0.8.4, WLED implements a powerful JSON API over HTTP.
+It is accessable using the `/json` subpage.
+
+### Obtaining light information
+Sending a GET request will return an object similar to the sample below.
+The response consists of four objects:
+- `state` contains the current state of the light. All values may be modified by the client (see below)
+- `info` contains general information about the device. No value can be modified using this API.
+- `effects` contains an array of the effect mode names
+- `palettes` contains an array of the palette names
+
+### Setting new values
+Sending a POST request to `/json/state` with (parts of) the state object will update the respective values.
+
+Sample JSON API response (v0.8.4):
 
 ```json
 {
@@ -61,7 +75,7 @@ Sample JSON API response (v0.8.4)
     "opt": 127,
     "brand": "WLED",
     "product": "DIY light",
-    "btype": "dev",
+    "btype": "src",
     "mac": "60019423b441"
   },
   "effects": [