add license application in OCR guide

Author: tony-xlh

_articles/extended-usage/ocr.md

@@ -16,7 +16,7 @@ Dynamic Web TWAIN provides an OCR add-on to extract text in your scanned images.
 ## Requirements
 
 * Windows 10 versions >= 1809 and all versions of Windows 11
-* A license with the OCR module
+* A license with the OCR module ([30-day trial application](https://www.dynamsoft.com/customer/license/trialLicense?product=dwt))
 
 ## How to Use