Added download and install information to README

Author: ghais

README.md

@@ -3,3 +3,8 @@ A Easy Digital Downloads plugin to associate 'Buy Now' guest users with their ex
 
 The plugin checks if the email address of a guest transaction matches that
 of someone in the database and associates the order with that user.
+
+Download and Install
+--------------------
+
+Download the plugin from https://github.com/convert/rekko-edd-buy-now/archive/v0.1.zip and unzip it in your wordpress' plugins directory