add main so installing from npm works

cli/package.json

@@ -4,6 +4,7 @@
 	"description": "SingleFile",
 	"author": "Gildas Lormeau",
 	"license": "AGPL-3.0-or-later",
+	"main": "single-file",
 	"dependencies": {
 		"file-url": "^3.0.0",
 		"iconv-lite": "^0.5.2",