There are several options. As Tom already mentioned, yiou can store text files as user objects. There is no tool support for user objects, however. This means you can't compare versions etc.
One thing you can do: compile the text files as methods into a class and store/version this class in the envy repository.
This way you can look at the text with Smalltalk Browsers and even search/diff etc.
You can even go further:
In one of our customer projects, we convert INI-Files to instances of a special class. This way we have tools to edit the ini files in the Smalltalk image and version changes to them. This allows for a great level of synchronisation of changes between developers, configuration of our deliverables and also for automation of file distribution. If you'd like to see this in action, you can watch it in a video of my talk at the VA Smalltalk Forum Europe 2010, available here: http://www.objektfabrik.de/Downloads/VASTForum2010/VFM10-04-GetBackToShapre-Tuchel.mp4
But I would only recommend these options if the text files aren't too big. I guess I'd rather not store MiB's of text files. It sure is better to use git, svn or any other file-based vcs if you need to store large files.