ci: drone: add notification step on exec runner

.drone.yml

@@ -14,4 +14,24 @@ steps:
 - name: test
   commands:
   - nix run 'nixpkgs#hello'
+- name: notify
+  comands:
+  - nix run 'github:ambroisie/matrix-notifier'
+  environment:
+    ADDRESS:
+      from_secret: matrix_homeserver
+    ROOM:
+      from_secret: matrix_roomid
+    USER:
+      from_secret: matrix_username
+    PASS:
+      from_secret: matrix_password
+    MESSAGE:
+      # FIXME: need to find a way to link
+      "Build ${DRONE_BUILD_STATUS} [${DRONE_REPO_OWNER}/${DRONE_REPO_NAME}](${DRONE_SYSTEM_PROTO}://${DRONE_SYSTEM_HOST}/${DRONE_REPO}/${DRONE_BUILD_NUMBER}) (${DRONE_BRANCH}) by ${DRONE_COMMIT_AUTHOR}"
+  settings:
+    trigger:
+      status:
+        - failure
+        - success
 ...