feat: Add yarn settings to handle dependencies

Yarn provides a good hablding of the dependencies
on top of npm, using yarn has been adopted not
only in the webpack project, but also lots of the
loaders. In order to keep consitency across
projects, adding it here also.

Author: DanielaValero

.gitignore

@@ -7,4 +7,7 @@
 node_modules
 
 # npm-debug log
-npm-debug.log
+npm-debug.log
+
+# yarn log
+yarn-error.log

package.json

@@ -11,6 +11,7 @@
   "bin": {
     "webpack-cli": "./bin/cli.js"
   },
+  "main": "./bin/cli.js",
   "scripts": {
     "lint": "eslint ./lib"
   },