Update part3b.md to mention the need of a credit card

Author: haplorhine

src/content/3/en/part3b.md

@@ -202,6 +202,8 @@ fly deploy
 
 #### Render
 
+<i>Note that you may need to give your credit card number to Render!</i>
+
 The following assumes that the [sign in](https://dashboard.render.com/) has been made with a GitHub account.
 
 After signing in, let us create a new "web service":