fix(README.md): installation instructions for OSX

Author: majg0

README.md

@@ -46,11 +46,18 @@ Table of contents
 Installation
 ============
 
+Linux
 ```bash
 $ wget https://raw.githubusercontent.com/ekalinin/github-markdown-toc/master/gh-md-toc
 $ chmod a+x gh-md-toc
 ```
 
+OSX
+```bash
+$ curl https://raw.githubusercontent.com/ekalinin/github-markdown-toc/master/gh-md-toc -o gh-md-toc
+$ chmod a+x gh-md-toc
+```
+
 Usage
 =====