Add email testing content (#2670)

* updated  105-qa-email-testing

* Update content/roadmaps/113-qa/content/105-qa-email-testing/readme.md

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

content/roadmaps/113-qa/content/105-qa-email-testing/readme.md

@@ -1 +1,6 @@
-# Qa email testing
+# Email Testing
+
+Email testing allows you to view your email before sending it out to your subscriber list to verify links, design, spelling errors, and more.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.campaignmonitor.com/blog/email-marketing/how-email-testing-and-rendering-works-and-why-its-important/'>About Email Testing</BadgeLink>