add .gitignore

.gitignore

@@ -0,0 +1,24 @@
+# Generated files
+package/generated*
+
+# Ignore installed npm modules
+node_modules/
+
+# Ignore build tool output, e.g. code coverage
+.nyc_output/
+coverage/
+docs/_data/coverage.json
+
+# Ignore API documentation
+api-docs/
+
+# Ignore folders from source code editors
+.vscode
+.idea
+
+# Ignore eleventy output when doing manual tests
+_site/
+
+# Ignore test files
+.cache
+test/stubs-layout-cache/_includes/*.js