fix(docs): make sure we can build the example rockcraft.yaml

Put the example code in a spread test, to ensure that we can always
build the example we give in the docs.

Fixes #399

docs/reference/code/example/rockcraft.yaml

@@ -0,0 +1,32 @@
+name: hello
+title: Hello World
+summary: An Hello World ROCK
+description: |
+  This is just an example of a Rockcraft project
+  for a Hello World ROCK.
+version: latest
+base: bare
+build-base: [email protected]
+license: Apache-2.0
+run-user: _daemon_
+environment:
+  FOO: bar
+services:
+  hello:
+    override: replace
+    command: /usr/bin/hello -t
+    environment:
+      VAR1: value
+      VAR2: "other value"
+platforms:
+  amd64:
+  armhf:
+    build-on: ["armhf", "arm64"]
+  ibm:
+    build-on: ["s390x"]
+    build-for: s390x
+parts:
+  hello:
+    plugin: nil
+    stage-packages:
+      - hello

docs/reference/code/example/task.yaml

@@ -0,0 +1,8 @@
+
+summary: Check that we can build the example rockcraft.yaml
+
+execute: |
+  rockcraft pack
+
+restore: |
+  rm -f ./*.rock

docs/reference/rockcraft.yaml.rst

@@ -223,41 +223,8 @@ The set of parts that compose the ROCK's contents
 Example
 =======
 
-.. code-block:: yaml
-
-  name: hello
-  title: Hello World
-  summary: An Hello World ROCK
-  description: |
-    This is just an example of a Rockcraft project
-    for a Hello World ROCK.
-  version: latest
-  base: bare
-  build-base: [email protected]
-  license: Apache-2.0
-  run-user: _daemon_
-  environment:
-    FOO: bar
-  services:
-    hello:
-      override: replace
-      command: /usr/bin/hello -t
-      environment:
-        VAR1: value
-        VAR2: "other value"
-  platforms:
-    amd64:
-    arm:
-      build-on: ["arm", "arm64"]
-    ibm:
-      build-on: ["s390x"]
-      build-for: s390x
-
-  parts:
-    hello:
-      plugin: nil
-      stage-packages:
-        - hello
+.. literalinclude:: code/example/rockcraft.yaml
+    :language: yaml
 
 
 .. _`Pebble Layer Specification format`:  https://github.com/canonical/pebble#layer-specification

docs/tutorials/code/node-app/task.yaml

@@ -1,5 +1,5 @@
 
-summary: donejs tutorial
+summary: nodejs tutorial
 
 execute: |
   # [docs:install-rockcraft]

spread.yaml

@@ -120,6 +120,9 @@ suites:
     systems:
     - ubuntu-22.04-64
 
+  docs/reference/code/:
+    summary: tests reference code from the docs
+
   tests/spread/general/:
     summary: tests for rockcraft core functionality