Update README.md (immutable-js#1150)

* Update README.md

update Using TypeScript with Immutable.js v4

* Update README.md

Update Using TypeScript with Immutable.js v4

* Update README.md

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* Update README.md

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Author: wisdomofgod

README.md

@@ -88,8 +88,8 @@ Use these Immutable collections and sequences as you would use native
 collections in your [Flowtype](https://flowtype.org/) or [TypeScript](http://typescriptlang.org) programs while still taking
 advantage of type generics, error detection, and auto-complete in your IDE.
 
-Installing `immutable` via npm brings with it type definitions for Flow and
-TypeScript, so you shouldn't need to do anything at all!
+Installing `immutable` via npm brings with it type definitions for Flow (v0.39.0 or higher)
+and TypeScript (v2.1.0 or higher), so you shouldn't need to do anything at all!
 
 #### Using TypeScript with Immutable.js v4
 
@@ -99,6 +99,14 @@ lib. Include either `"target": "es2015"` or `"lib": "es2015"` in your
 `tsconfig.json`, or provide `--target es2015` or `--lib es2015` to the
 `tsc` command.
 
+```js
+import { Map } from "immutable";
+const map1 = Map({ a: 1, b: 2, c: 3 });
+const map2 = map1.set('b', 50);
+map1.get('b'); // 2
+map2.get('b'); // 50
+```
+
 #### Using TypeScript with Immutable.js v3 and earlier:
 
 Previous versions of Immutable.js include a reference file which you can include