Merge pull request progit#1489 from HonkingGoose/tip-git-send-email-io

Add tip section with link to git-send-email.io

Author: ben

book/05-distributed-git/sections/contributing.asc

@@ -785,6 +785,11 @@ References: <y>
 Result: OK
 ----
 
+[TIP]
+====
+For help on confuring your system and email, more tips and tricks, and a sandbox to send a trial patch via email, go to [git-send-email.io](https://git-send-email.io/).
+====
+
 ==== Summary
 
 In this section, we covered multiple workflows, and talked about the differences between working as part of a small team on closed-source projects vs contributing to a big public project.