Add ReactNode type docs (#627)

Author: filiptammergard

docs/react-types/ReactNode.md

@@ -0,0 +1,50 @@
+---
+title: ReactNode
+---
+
+`ReactNode` is a type that describes what React can render.
+
+## Parameters
+
+`ReactNode` does not take any parameters.
+
+## Usage
+
+### Typing `children`
+
+The most common use case for `ReactNode` is typing `children`.
+
+```tsx
+import { ReactNode } from "react";
+
+interface Props {
+  children?: ReactNode;
+}
+
+function Component({ children }: Props) {
+  return children;
+}
+```
+
+`<Component>` accepts anything that React can render as `children`. Here are some examples:
+
+```tsx
+function Examples() {
+  return (
+    <>
+      <Component>
+        <div>Hello</div>
+      </Component>
+      <Component>Hello</Component>
+      <Component>{123}</Component>
+      <Component>
+        <>Hello</>
+      </Component>
+      <Component>{true}</Component>
+      <Component>{null}</Component>
+      <Component>{undefined}</Component>
+      <Component>{[1, 2, 3]}</Component>
+    </>
+  );
+}
+```

docs/react-types/index.md

@@ -5,3 +5,4 @@ title: React Types
 `@types/react` makes some types available that can be very useful. Here's a list in alphabetical order with links to the detailed reference pages.
 
 - [`ComponentProps<ElementType>`](/docs/react-types/ComponentProps)
+- [`ReactNode`](/docs/react-types/ReactNode)