ci: add workflow to publish docker image

.github/workflows/docker.yml

@@ -0,0 +1,20 @@
+name: Publish Docker image
+on:
+  release:
+    types: [published]
+
+jobs:
+  push_to_registry:
+    name: Push Docker image to Docker Hub
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out the repo
+        uses: actions/checkout@v2
+      - name: Push to Docker Hub
+        uses: docker/build-push-action@v1
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+          repository: nadoo/glider
+          tag_with_ref: true
+          

README.md

@@ -363,7 +363,7 @@ glider -config CONFIGPATH -listen :8080 -verbose
 
 ## Links
 
-- [ipset](https://github.com/nadoo/ipset): ipset package for Go via netlink socket
-- [conflag](https://github.com/nadoo/conflag): command line and config file parse support
-- [ArchLinux](https://www.archlinux.org/packages/community/x86_64/glider): a great linux distribution with glider pre-built package
-- [urlencode](https://www.w3schools.com/tags/ref_urlencode.asp): you should encode special characters in  scheme url. e.g: `@`->`%40`
+- [ipset](https://github.com/nadoo/ipset): ipset package for Go via netlink socket.
+- [conflag](https://github.com/nadoo/conflag): a drop-in replacement for Go's standard flag package with config file support.
+- [ArchLinux](https://www.archlinux.org/packages/community/x86_64/glider): a great linux distribution with glider pre-built package.
+- [urlencode](https://www.w3schools.com/tags/ref_urlencode.asp): you should encode special characters in scheme url. e.g: `@`->`%40`