Add build script

ecs/README.md

@@ -134,7 +134,7 @@ docker build -t ejabberd/ecs .
 Build ejabberd Community Server base image for a given ejabberd version:
 
 ```bash
-docker build --build-arg VERSION=18.01 -t ejabberd/ecs:18.01 .
+./build.sh 18.03
 ```
 
 ### TODO

ecs/build.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+
+current=$(date +%y.%m)
+version=${1:-$current}
+
+docker build --build-arg VERSION=$version -t ejabberd/ecs:$version .
+docker tag ejabberd/ecs:$version ejabberd/ecs:latest