How to add text or description in a form without writing a module?
You are on the right track:


Create a new field in your content type of type "Long Text", call it something like Ingredients Text ("ingredients_text") for the machine name --  the text that will be within this field can change per node as you like.
Then, go to your Dependencies tab in this content type. 
Click "Add new dependency" and choose your newly created Textfield as the "Dependent".  Choose your select / radio button as the "Dependee". (Leave the other two settings as is.)
Click "Add Dependency"
You are in a new screen, take the defaults
For Node View setting of the edit screen, try "Hide the dependent if the dependee is not viewable by the user and the dependency is not triggered". 
Now when you the user is in the node, he can choose the radio button and the new text field will appear!


You will need to play with the settings but this does work, I just set this up on a site for a client.  Note, the options in step 6 may vary depending on your particular setup.