git commit -m 'Issue #3521420 by dcam: Add composer.json'

composer.json

+{
+    "name": "drupal/styleguide",
+    "type": "drupal-module",
+    "description": "Generates a theme style guide for proofing common elements",
+    "keywords": ["Drupal"],
+    "license": "GPL-2.0+",
+    "homepage": "https://www.drupal.org/project/styleguide",
+    "authors": [
+        {
+            "name": "agentrickard",
+            "homepage": "https://www.drupal.org/u/agentrickard",
+            "role": "Maintainer"
+        },
+        {
+            "name": "bevan",
+            "homepage": "https://www.drupal.org/u/bevan",
+            "role": "Maintainer"
+        },
+        {
+            "name": "dave-reid",
+            "homepage": "https://www.drupal.org/u/dave-reid",
+            "role": "Maintainer"
+        },
+        {
+            "name": "dcam",
+            "homepage": "https://www.drupal.org/u/dcam",
+            "role": "Maintainer"
+        },
+        {
+            "name": "dead_arm",
+            "homepage": "https://www.drupal.org/u/dead_arm",
+            "role": "Maintainer"
+        },
+        {
+            "name": "geerlingguy",
+            "homepage": "https://www.drupal.org/u/geerlingguy",
+            "role": "Maintainer"
+        },
+        {
+            "name": "greg-boggs",
+            "homepage": "https://www.drupal.org/u/greg-boggs",
+            "role": "Maintainer"
+        },
+        {
+            "name": "irakli",
+            "homepage": "https://www.drupal.org/u/irakli",
+            "role": "Maintainer"
+        },
+        {
+            "name": "markabur",
+            "homepage": "https://www.drupal.org/u/markabur",
+            "role": "Maintainer"
+        },
+        {
+            "name": "mfer",
+            "homepage": "https://www.drupal.org/u/mfer",
+            "role": "Maintainer"
+        },
+        {
+            "name": "oleksiy",
+            "homepage": "https://www.drupal.org/u/oleksiy",
+            "role": "Maintainer"
+        },
+        {
+            "name": "psynaptic",
+            "homepage": "https://www.drupal.org/u/psynaptic",
+            "role": "Maintainer"
+        }
+    ],
+    "support": {
+        "issues": "https://www.drupal.org/project/issues/styleguide",
+        "source": "https://git.drupalcode.org/project/styleguide"
+    }
+}