Support markdown report in Gradle plugin (#4995)

* Support markdown report in Gradle plugin

* Add markdown description to website docs

* Improve markdown description for website docs

README.md

@@ -76,6 +76,7 @@ tasks.withType<Detekt>().configureEach {
         xml.required.set(true) // checkstyle like format mainly for integrations like Jenkins
         txt.required.set(true) // similar to the console output, contains issue signature to manually edit baseline files
         sarif.required.set(true) // standardized SARIF format (https://sarifweb.azurewebsites.net/) to support integrations with Github Code Scanning
+        md.required.set(true) // simple Markdown format
     }
 }