Add an external link to Raspberry PI tutorial (#13)

Also fixed page title spelling and polished page description.

Author: rousskov

docs/ExternalLinks.md

@@ -1,16 +1,18 @@
 ---
 ---
-# External resoruces and links
+# External resources and links
 
-Here go resources to external sites which might be of interest to
-developers and users.
+These external sites may be of interest to developers and users.
 
 ## Introductory
 
 - <http://kenttongmo.blogspot.it/2013/03/concepts-of-squid.html>
 :   An introductory article by Kent Tong to core proxy and
     reverse-proxy concepts, with some clear examples for squid
 
+- [How to Setup a Proxy Server with Squid and Raspberry PI](https://peppe8o.com/setup-a-proxy-server-with-raspberry-pi-os-lite-and-squid/)
+:   Giuseppe Cassibba shows how to install Squid on Raspberry PI.
+
 ## For developers
 
 - <http://blogs.msdn.com/ie/archive/2005/10/22/483795.aspx>