README: Example how to mount an application (#45)

Author: andys8

README.md

@@ -8,3 +8,31 @@
 </a>
 
 This library contains the [React Basic](https://github.com/lumihq/purescript-react-basic) DOM modules.
+
+## Example
+
+```purescript
+import Prelude
+
+import Data.Maybe (Maybe(..))
+import Effect (Effect)
+import Effect.Exception (throw)
+import React.Basic.DOM.Client (createRoot, renderRoot)
+import React.Basic.DOM (text)
+import Web.DOM.NonElementParentNode (getElementById)
+import Web.HTML (window)
+import Web.HTML.HTMLDocument (toNonElementParentNode)
+import Web.HTML.Window (document)
+
+main :: Effect Unit
+main = do
+  doc <- document =<< window
+  root <- getElementById "root" $ toNonElementParentNode doc
+  case root of
+    Nothing -> throw "Could not find container element"
+    Just container -> do
+      reactRoot <- createRoot container
+      renderRoot reactRoot (text "Hello")
+```
+
+More examples can be found in the [PureScript Cookbook](https://github.com/JordanMartinez/purescript-cookbook/tree/master/recipes).