Add documentation coverage badge to README

Author: Mordil

.gitignore

@@ -23,6 +23,7 @@ xcuserdata/
 *.xccheckout
 *.xcscmblueprint
 *.xcodeproj
+public/
 
 ## Obj-C/Swift specific
 *.hmap

README.md

@@ -10,6 +10,7 @@
 
 <p>
     <a href="https://gitlab.com/Mordil/swift-redi-stack/pipelines"><img src="https://gitlab.com/Mordil/swift-redi-stack/badges/master/pipeline.svg" alt="Build Status"></a>
+    <a href="https://docs.redistack.info"><img src="https://docs.redistack.info/badge.svg" alt="Documentation Coverage"></a>
     <a href="https://codeclimate.com/github/Mordil/swift-redi-stack/maintainability"><img src="https://api.codeclimate.com/v1/badges/3ff84c8d384b01cb5875/maintainability" /></a>
 </p>
 </div>