feat: setup CI with drone

.drone.yml

@@ -0,0 +1,34 @@
+---
+kind: pipeline
+name: coopcloud.tech/tagcmp
+steps:
+  - name: make check
+    image: golang:1.17
+    commands:
+      - make check
+
+  - name: make build
+    image: golang:1.17
+    commands:
+      - make build
+
+  - name: make test
+    image: golang:1.17
+    commands:
+      - make test
+
+  - name: notify on failure
+    image: plugins/matrix
+    settings:
+      homeserver: https://matrix.autonomic.zone
+      roomid: "IFazIpLtxiScqbHqoa:autonomic.zone"
+      userid: "@autono-bot:autonomic.zone"
+      accesstoken:
+        from_secret: autono_bot_access_token
+    depends_on:
+      - make check
+      - make build
+      - make test
+    when:
+      status:
+        - failure

Makefile

@@ -0,0 +1,8 @@
+build:
+	@go build .
+
+check:
+	@test -z $$(gofmt -l .) || (echo "gofmt: formatting issue - run 'make format' to resolve" && exit 1)
+
+test:
+	@go test . -cover

README.md

@@ -1,5 +1,6 @@
 # tagcmp
 
+[![Build Status](https://build.coopcloud.tech/api/badges/coop-cloud/tagcmp/status.svg?ref=refs/heads/main)](https://build.coopcloud.tech/coop-cloud/tagcmp)
 [![Go Report Card](https://goreportcard.com/badge/git.coopcloud.tech/coop-cloud/tagcmp)](https://goreportcard.com/report/git.coopcloud.tech/coop-cloud/tagcmp)
 
 Comparison operations for image tags. Because registries aren't doing this for