[INTERNAL] package.json: Define files to publish

- index.js and lib/ content is required runtime code.
- CONTRIBUTING.md should guide people on where to find the source/
report issues.
- jsdoc.json is required to generate cross-repo API doc for releases
(currently done in SAP/ui5-tooling)

package.json

@@ -34,6 +34,12 @@
 		"release-note": "git-chglog -c .chglog/release-config.yml v$npm_package_version",
 		"report-coveralls": "nyc report --reporter=text-lcov | coveralls"
 	},
+	"files": [
+		"index.js",
+		"CONTRIBUTING.md",
+		"jsdoc.json",
+		"lib/**"
+	],
 	"ava": {
 		"files": [
 			"test/lib/**/*.js"