[react] [readme] fix broken React doc links and Foo syntax error

Author: mohit-nayak

react/README.md

@@ -25,7 +25,7 @@ This style guide is mostly based on the standards that are currently prevalent i
 ## Basic Rules
 
   - Only include one React component per file.
-    - However, multiple [Stateless, or Pure, Components](https://facebook.github.io/react/docs/reusable-components.html#stateless-functions) are allowed per file. eslint: [`react/no-multi-comp`](https://github.com/jsx-eslint/eslint-plugin-react/blob/master/docs/rules/no-multi-comp.md#ignorestateless).
+    - However, multiple [Stateless, or Pure, Components](https://legacy.reactjs.org/docs/components-and-props.html#function-and-class-components) are allowed per file. eslint: [`react/no-multi-comp`](https://github.com/jsx-eslint/eslint-plugin-react/blob/master/docs/rules/no-multi-comp.md#ignorestateless).
   - Always use JSX syntax.
   - Do not use `React.createElement` unless you’re initializing the app from a file that is not JSX.
   - [`react/forbid-prop-types`](https://github.com/jsx-eslint/eslint-plugin-react/blob/master/docs/rules/forbid-prop-types.md) will allow `arrays` and `objects` only if it is explicitly noted what `array` and `object` contains, using `arrayOf`, `objectOf`, or `shape`.
@@ -75,7 +75,7 @@ This style guide is mostly based on the standards that are currently prevalent i
 
 ## Mixins
 
-  - [Do not use mixins](https://facebook.github.io/react/blog/2016/07/13/mixins-considered-harmful.html).
+  - [Do not use mixins](https://legacy.reactjs.org/blog/2016/07/13/mixins-considered-harmful.html).
 
   > Why? Mixins introduce implicit dependencies, cause name clashes, and cause snowballing complexity. Most use cases for mixins can be accomplished in better ways via components, higher-order components, or utility modules.
 
@@ -454,7 +454,7 @@ We don’t recommend using indexes for keys if the order of items may change.
   - Spreading objects with known, explicit props. This can be particularly useful when testing React components with Mocha’s beforeEach construct.
 
   ```jsx
-  export default function Foo {
+  export default function Foo() {
     const props = {
       text: '',
       isPublished: false
@@ -735,7 +735,7 @@ We don’t recommend using indexes for keys if the order of items may change.
 
   > Why? [`isMounted` is an anti-pattern][anti-pattern], is not available when using ES6 classes, and is on its way to being officially deprecated.
 
-  [anti-pattern]: https://facebook.github.io/react/blog/2015/12/16/ismounted-antipattern.html
+  [anti-pattern]: https://legacy.reactjs.org/blog/2015/12/16/ismounted-antipattern.html
 
 ## Translation