Update README.md

Author: sdgluck

README.md

@@ -6,6 +6,7 @@
 
 - Build & learn about the Cache-Control header and its directives
 - Generates example library code for setting headers, e.g. nginx, express, & others
+- Share header configurations via shareable URLs (e.g. [public + max-age 2 days](https://cache-control.sdgluck.now.sh/?s=W3sibmFtZSI6InB1YmxpYyIsImFyZyI6bnVsbCwidGltZSI6InNlY3MifSx7Im5hbWUiOiJtYXgtYWdlIiwiYXJnIjoiMiIsInRpbWUiOiJkYXlzIn1d))
 - Header descriptions taken from [MDN](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control)
 
 <img src="https://raw.githubusercontent.com/sdgluck/cache-control/master/screenshot.jpg" />