docs: Update ci.md

Add drone instructions.

www/content/ci.md

@@ -70,3 +70,29 @@ deployment:
     commands:
       - curl -sL https://git.io/goreleaser | bash
 ```
+
+# Drone
+
+By default, drone does not fetch tags. `plugins/git` is used with default values, in most of the case we'll need overwrite the `clone` step with tags enabled in order to make `goreleaser` work correctly.
+In this example we're creating a new release every time a new tag is pushed.
+Note that you'll need to enable `tags` in repo settings and add `github_token` secret.
+
+```yml
+pipeline:
+  clone:
+    image: plugins/git
+    tags: true
+
+  test:
+    image: golang:1.10
+    commands:
+      - go test ./... -race
+
+  release:
+    image: golang:1.10
+    secrets: [github_token]
+    commands:
+      curl -sL https://git.io/goreleaser | bash
+    when:
+      event: tag
+```