ci: woodpecker: add exec pipeline

.woodpecker/docker.yml

@@ -0,0 +1,6 @@
+labels:
+  type: docker
+
+pipeline:
+- name: test
+  image: hello-world

.woodpecker/exec.yml

@@ -0,0 +1,26 @@
+labels:
+  type: exec
+
+pipeline:
+- name: test
+  image: bash
+  commands:
+  - nix run 'nixpkgs#hello'
+
+- name: notify
+  image: bash
+  secrets:
+  - source: matrix_homeserver
+    target: address
+  - source: matrix_roomid
+    target: room
+  - source: matrix_username
+    target: user
+  - source: matrix_password
+    target: pass
+  commands:
+  - nix run 'github:ambroisie/matrix-notifier'
+  when:
+    status:
+    - failure
+    - success