Add Docker build badge to README.md

Change-Id: I8577bed7294511896338ac5a6db397b0fd03ee0c

.github/workflows/ci.yml

@@ -2,10 +2,14 @@ name: CI
 on:
   push:
     paths-ignore:
-      - 'docs/**'
       - '*.conf.sample*'
-      - '*.md'
+      - 'Dockerfile'
+      - '.dockerignore'
+      - 'docs/**'
+      - '.editorconfig'
+      - '.gitignore'
       - '.mailmap'
+      - '*.md'
   workflow_dispatch:
 
 permissions: {}

README.md

@@ -6,10 +6,11 @@
 
 </div>
 
+![Latest version](https://img.shields.io/github/v/tag/named-data/ndn-cxx?label=Latest%20version)
+![Language](https://img.shields.io/badge/C%2B%2B-17-blue)
 [![CI](https://github.com/named-data/ndn-cxx/actions/workflows/ci.yml/badge.svg)](https://github.com/named-data/ndn-cxx/actions/workflows/ci.yml)
+[![Docker](https://github.com/named-data/ndn-cxx/actions/workflows/docker.yml/badge.svg)](https://github.com/named-data/ndn-cxx/actions/workflows/docker.yml)
 [![Docs](https://github.com/named-data/ndn-cxx/actions/workflows/docs.yml/badge.svg)](https://github.com/named-data/ndn-cxx/actions/workflows/docs.yml)
-![Language](https://img.shields.io/badge/C%2B%2B-17-blue)
-![Latest version](https://img.shields.io/github/v/tag/named-data/ndn-cxx?label=Latest%20version)
 
 **ndn-cxx** is a C++17 library implementing Named Data Networking (NDN) primitives
 that can be used to write various NDN applications. The library is currently being