Specify that WHITELIST is an optional parameter

Author: sagidM

README.md

@@ -138,10 +138,10 @@ or
 * * **Function code -> Code entry type -> Upload a .zip file** upload a zip file
 * * In **Runtime**, select the latest version of Node.js that you found on [Releases](https://github.com/sagidM/s3-resizer/releases)
 * * [You can now click on **Save** to save your time because it takes a while to upload a zip file]
-* * Set up these three **Environment variables** _(format: key=value)_  
+* * Set up the following **Environment variables** _(format: key=value)_  
 **BUCKET**=_your bucket's name_  
 **URL**=**Endpoint** you copied before (from Static website hosting)  
-**WHITELIST**= your list (space-separated) of allowed size options (e.g. AUTOx150 300x200 100x100_max)  
+**WHITELIST**=your list (space-separated) of allowed size options (e.g. AUTOx150 300x200 100x100_max). This parameter is optional, if not provided, the lambda will process everything  
 * * In **Basic settings**
 * * * Allocate 768mb memory
 * * * Timeout could be 5 seconds