added codesandbox stuff

.codesandbox/template.json

@@ -0,0 +1,18 @@
+{
+	"title": "mutableJS / demo - Mini Todo App",
+	"description": "A mini todo app written using mutableJS.",
+	"tags": [
+		"typescript",
+		"jsx",
+		"signals",
+		"reactivity",
+		"mutability",
+		"DOM",
+		"mutableJS",
+		"hyperMedia",
+		"HyperText",
+		"Website",
+		"Webapp"
+	],
+	"published": true
+}

README.md

@@ -11,6 +11,10 @@ Demo repo: Simple ToDo-app written with [@mutablejs/core](https://www.npmjs.com/
 
 This is a proof of concept of the reactive mutability of DOM elements accomplished with the use of `@mutablejs/core` and `@mutablejs/dom`
 
+#### Try before using
+
+You can [try it out in CodeSandbox](https://codesandbox.io/p/sandbox/github/mutableJS/demo/tree/master?file=%2Fsrc%2Findex.tsx%3A1%2C1) before you clone and start using our demo app.
+
 ## Installation and Startup
 
 With **npm**: