Merge pull request keithamus#3 from keithamus/add-basic-readme

add basic readme

Author: keithamus

README.md

@@ -0,0 +1,61 @@
+# Observable Polyfill
+
+This polyfills the DOM `Observable` class, as well as `EventTarget.prototype.when`.
+
+To see the explainer of these, please visit https://github.com/WICG/observable.
+
+## Installation
+
+### With npm
+
+If you're using npm, you only need to import the package, like so:
+
+```js
+import "observable-polyfill";
+```
+
+This will automatically apply the polyfill if required.
+
+If you'd like to manually apply the polyfill, you can instead import the `isSupported` and `apply` functions directly from the `./observable.js` file, which
+is mapped to `/fn`:
+
+```js
+import { isSupported, apply } from "observable-polyfill/fn";
+if (!isSupported()) apply();
+```
+
+An `isPolyfilled` function is also available, to detect if it has been polyfilled:
+
+```js
+import { isSupported, isPolyfilled, apply } from "observable-polyfill/fn";
+if (!isSupported() && !isPolyfilled()) apply();
+```
+
+Alternatively, if you're not using a package manager, you can use the `unpkg` script:
+
+```html
+<!-- polyfill automatically -->
+<script
+  type="module"
+  async
+  src="https://unpkg.com/observable-polyfill@latest/observable.min.js"
+></script>
+```
+
+```html
+<!-- polyfill manually -->
+<script type="module" async>
+  import {isSupported, apply} from "https://unpkg.com/observable-polyfill@latest/observable.js"
+  if (!isSupported()) apply();
+</script>
+```
+
+## Usage
+
+With the module imported, you can start to use `Observable` and `.when`:
+
+```js
+new Observable(...)
+
+document.body.when('click').take(1).subscribe(console.log)
+```