build: Tweak Mergify conditions and add Mergify badge

Author: jakubjanecek

.mergify.yml

@@ -18,6 +18,8 @@ pull_request_rules:
   - name: automatic merge on CI success and review
     conditions:
       - base=master
+      - "#review-requested=0"
+      - "#changes-requested-reviews-by=0"
       - "#approved-reviews-by>=1"
       - status-success=Travis CI - Pull Request
     actions:

README.md

@@ -3,6 +3,7 @@
 [![Build Status](https://travis-ci.org/avast/scala-server-toolkit.svg?branch=master)](https://travis-ci.org/avast/scala-server-toolkit)
 [![Maven Central](https://img.shields.io/maven-central/v/com.avast/sst-bundle-zio-http4s-blaze_2.12)](https://repo1.maven.org/maven2/com/avast/sst-bundle-zio-http4s-blaze_2.12/)
 [![Scala Steward badge](https://img.shields.io/badge/Scala_Steward-helping-brightgreen.svg?style=flat&logo=data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAA4AAAAQCAMAAAARSr4IAAAAVFBMVEUAAACHjojlOy5NWlrKzcYRKjGFjIbp293YycuLa3pYY2LSqql4f3pCUFTgSjNodYRmcXUsPD/NTTbjRS+2jomhgnzNc223cGvZS0HaSD0XLjbaSjElhIr+AAAAAXRSTlMAQObYZgAAAHlJREFUCNdNyosOwyAIhWHAQS1Vt7a77/3fcxxdmv0xwmckutAR1nkm4ggbyEcg/wWmlGLDAA3oL50xi6fk5ffZ3E2E3QfZDCcCN2YtbEWZt+Drc6u6rlqv7Uk0LdKqqr5rk2UCRXOk0vmQKGfc94nOJyQjouF9H/wCc9gECEYfONoAAAAASUVORK5CYII=)](https://scala-steward.org)
+[![Mergify badge](https://img.shields.io/endpoint.svg?url=https://gh.mergify.io/badges/avast/scala-server-toolkit)](https://mergify.io)
 
 This project is a culmination of years of Scala development at Avast and tries to represent the best practices of Scala server development 
 we have gained together with tools that allow us to be effective. It is a set of small, flexible and cohesive building blocks that fit