write readme

README.md

@@ -1,2 +1,21 @@
 grunt-filesize
-==============
+==============
+
+log file size
+
+## Documentation
+modify your `grunt.js` file by adding the following line:
+
+    grunt.loadNpmTasks('grunt-filesize');
+
+Then add some configuration for the plugin like so:
+
+    grunt.initConfig({
+        ...
+        filesize: {
+          base: {
+            files: ['build/*.js']
+          }
+        },
+        ...
+    });