Unfortunately, I cannot give you any answer to adding a text file to the home screen without jailbreak. The answer above should tend to your jailbreak needs. But, if you are interested in how to add a text file to the Safari bookmark menu, read on.
Nothing is actually stored on the home screen. It just links to the apps and web links. But, you use PlainText. So you can do this:
- Open Safari and navigate to any webpage,
about:blank will do.
- Save the page as bookmark. Not home screen icon. Bookmark.
- Find your bookmark from the menus. Tap Edit, and click the arrow on the bookmark's right end.
- Edit the address on the bookmark to:
Now you have a bookmark that will take you straight to a text file.
For more info on the PlainText URL Scheme, in-app, navigate to Settings > Help > PlainText URL Scheme.