Add tslib to installation instructions (#253)

* Add tslib to installation instructions for yarn

Author: brandon-leapyear

README.md

@@ -16,9 +16,9 @@ This version is somewhat slower than original, but it will print out typescript
 
 ```bash
 # with npm
-npm install rollup-plugin-typescript2 typescript --save-dev
+npm install rollup-plugin-typescript2 typescript tslib --save-dev
 # with yarn
-yarn add rollup-plugin-typescript2 typescript --dev
+yarn add rollup-plugin-typescript2 typescript tslib --dev
 ```
 
 ## Usage