[DEPS] Make TypeScript a peerDependency (#265)

Author: j-f1

README.md

@@ -12,13 +12,19 @@ TypeScript support for ESLint. (This is still in the very early stages, so pleas
 
 You'll first need to install [ESLint](http://eslint.org):
 
-```
+```shellsession
 $ npm i eslint --save-dev
 ```
 
-Last, install `eslint-plugin-typescript`:
+Next, install `typescript` if you haven’t already:
 
+```shellsession
+$ npm i typescript@~3.1.1 --save-dev
 ```
+
+Last, install `eslint-plugin-typescript`:
+
+```shellsession
 $ npm install eslint-plugin-typescript --save-dev
 ```
 

package.json

@@ -46,7 +46,8 @@
     "typescript": "~3.1.1"
   },
   "peerDependencies": {
-    "eslint": ">=4.13.1 < 6"
+    "eslint": ">=4.13.1 < 6",
+    "typescript": "~3.1.1"
   },
   "nyc": {
     "include": [