Update sentence-alignment.md

As suggested by doc review team, 
(1) Line 52: It would be best to format the content "It's important to note that:" (and the list that follows) by using a custom Markdown element to create an alert box. Use the extension syntax:
   > [!NOTE]
   > Text goes on next line...

(2) removed en-us from URL

Author: melghazali

articles/cognitive-services/Translator/custom-translator/sentence-alignment.md

@@ -50,10 +50,11 @@ For a training to succeed, the table below shows the minimum number of sentences
 | Testing*    | 5,000                                      | 2,500                          |
 | Dictionary | 0                                          | No upper limit                 |
 
-*It’s important to note:
-- Training will not start and will fail if the 10,000 minimum sentence count for Training is not met. 
-- Tuning and Testing are optional. If you do not provide them, the system will remove an appropriate percentage from Training to use for validation and testing. 
-- You can train a model using only dictionary data. Please refer to [What is Dictionary](https://docs.microsoft.com/en-us/azure/cognitive-services/translator/custom-translator/what-is-dictionary).
+> [!NOTE]
+> *It’s important to note:
+> - Training will not start and will fail if the 10,000 minimum sentence count for Training is not met. 
+> - Tuning and Testing are optional. If you do not provide them, the system will remove an appropriate percentage from Training to use for validation and testing. 
+> - You can train a model using only dictionary data. Please refer to [What is Dictionary](https://docs.microsoft.com/azure/cognitive-services/translator/custom-translator/what-is-dictionary).
 
 ## Next steps