Add functional testing docs (#1664)

* Update readme.md

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* Update content/roadmaps/113-qa/content/100-qa-basics/107-testing-techniques/100-functional-testing/readme.md

* Update content/roadmaps/113-qa/content/100-qa-basics/107-testing-techniques/100-functional-testing/readme.md

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

content/roadmaps/113-qa/content/100-qa-basics/107-testing-techniques/100-functional-testing/readme.md

@@ -1 +1,7 @@
-# Functional testing
+# Functional Testing
+
+Functional testing is a type of software testing that validates the software system against the functional requirements/specifications. The purpose of Functional tests is to test each function of the software application by providing appropriate input and verifying the output against the Functional requirements.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.guru99.com/functional-testing.html'>What is Functional Testing? Types & Examples</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.browserstack.com/guide/functional-testing'>Functional Testing : A Detailed Guide</BadgeLink>