Update README.md

Author: mistermantas

README.md

@@ -4,6 +4,21 @@
 
 **This is a work in progres. Playkit for developers.**
 
+## Prerequisites
+
+* You have a cState status page set up with a [read-only API](https://github.com/cstate/cstate/wiki/API)
+* You have modified your headers (for Netlify users, it's the `netlify.toml` file in the root) to allow for cross-origin access
+* Your browser (or environment) supports `fetch()`
+
+The demo page uses this for its `netlify.toml`:
+
+```toml
+[[headers]]
+    for = "/*.json"
+    [headers.values]
+      Access-Control-Allow-Origin = "*"
+```
+
 ## License
 
 The idea for this project was [originally inspired](https://github.com/cstate/cstate/issues/131) by the GitHub / cState user @ririko5834.