Many people don't seem to know any more what a text file is. Windows kind of "encourages" use of Word format .doc files, so that's probably the reason. But plain ASCII text has the advantage of being almost universal. Almost all text editors and word processors can load and save ASCII text files. Also, our file library's online file view function can display text files within your uploads so people can read your docs before downloading.
Creating a text file is hardly a challenge. Use whatever text editor you normally use. The file type is determined only when you save it. For most text editors you will have to use the "Save As" function in the File menu and then choose the file type. It may be referred to as "ASCII", "text", "MS-DOS text" or some variation. You may have to refer to your editor's docs or help file to determine the correct choice. Here are some of the common ones:
Word Pad: "Text Document - MS-DOS Format"
Note Pad: "All Files (*.*)"
Warning: Some programs, Note Pad for example, may not respect the file name you choose! You'll tell it to save under the name "file_id.diz" but it will ignore you and use something like "file_id.diz.txt" instead. Because of this you will need to check the actual name of the file you ended up with, and rename it if necessary (you can use Windows Explorer to rename files), before adding it to your zip file to make sure it really got the name you wanted.
It also sometimes depends on what options you choose. For example, if you use Note Pad and do a "save as" and choose "Text Documents" it will always add .txt to the end of your chosen file name.