Amend documentation to install globally

Author: slavaaaaaaaaaa

README.md

@@ -30,7 +30,7 @@ _(TOC generated by [verb](https://github.com/verbose/verb) using [markdown-toc](
 Install with [npm](https://www.npmjs.com/):
 
 ```sh
-$ npm install --save markdown-toc
+$ npm install -g markdown-toc
 ```
 
 ## CLI
@@ -356,4 +356,4 @@ Released under the [MIT License](LICENSE).
 
 ***
 
-_This file was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme), v0.6.0, on September 19, 2017._
+_This file was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme), v0.6.0, on September 19, 2017._