Goreleaser config (#37)

.goreleaser.yml

+builds:
+  - main: main.go
+    binary: acme-dns
+    env:
+      - CGO_ENABLED=1
+    goos:
+      - linux
+      - darwin
+      - windows
+      - freebsd
+      - netbsd
+      - openbsd
+    goarch:
+      - 386
+      - amd64
+      - arm
+      - arm64
+    ignore:
+      - goos: darwin
+        goarch: 386
+      - goos: darwin
+        goarch: arm
+      - goos: darwin
+        goarch: arm64
+
+archive:
+  format: tar.gz
+  format_overrides:
+    - goos: windows
+      format: zip
+    - goos: darwin
+      format: zip
+  replacements:
+    amd64: 64bit
+    386: 32bit
+    darwin: macOS
+  files:
+    - LICENSE
+    - README.md
+    - Dockerfile
+    - config.cfg