[meta] add exports

This is theoretically non-breaking, because v4.1.0 only had one JS file, the main

Author: ljharb

package.json

@@ -7,6 +7,10 @@
 	},
 	"license": "MIT",
 	"main": "index.js",
+	"exports": {
+		".": "./index.js",
+		"./package.json": "./package.json"
+	},
 	"sideEffects": false,
 	"repository": {
 		"type": "git",