fix(ft): give more failproof example in README

Without that `ssl` defaults to being disabled, and interacting
with AWS S3 with such configuration consistently times out.

apps/emqx_ft/README.md

@@ -56,10 +56,13 @@ file_transfer {
         s3 {
           enable = true
           host = "s3.us-east-1.amazonaws.com"
-          port = "443"
+          port = 443
           access_key_id = "AKIA27EZDDM9XLINWXFE"
           secret_access_key = "..."
           bucket = "my-bucket"
+          transport_options = {
+            ssl { enable = true }
+          }
         }
       }
     }