Add password reqs to known issues

Author: mikewill4

articles/storage/blobs/secure-file-transfer-protocol-known-issues.md

@@ -74,6 +74,8 @@ The following clients are known to be incompatible with SFTP for Azure Blob Stor
 ## Security
 
 - Host keys are published [here](secure-file-transfer-protocol-host-keys.md). During the public preview, host keys may rotate frequently.
+  
+- User supplied passwords are not supported. Passwords are generated by Azure and minimum 88 characters in length.
 
 ## Integrations