Issue on page /mastering-plone/dexterity_2_talk.html 12.1 file already exists

In 12.1 you are told to create a file types.xml in profile/default but the file already exists. I think either deleting the file in the "initial" branch would make it more clear or changing the task to just add the 
```
<object name="talk" meta_type="Dexterity FTI"/>
```
into the existing types.xml.