Reading Usable Help
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Gordon R. Meyer
The classic "Read Me" file is a holdover from the early days of computing. Back when software came with printed documentation, a text file was put on the diskette (or tape) containing corrections and additions for the manual. It was truly "late-breaking news" that didn't make it into print. In the non-commercial realm, the text file was likely the only documentation. In both cases, the Alice In Wonderland-ish name "Read Me" made a lot of sense. Ignore the contents of the document at your own peril.
But in more recent years read me files are more likely ignored, with no ill effect, since their content is often unfocused and redundant. I think that read me files are most effective when they only contain information that user's truly need before using the software. That is, installation instructions and caveats. If the software is freely distributed, and there's a chance that the user might not know what the software does, a brief description of its purpose is also useful. Everything else -- task instruction, tutorials, descriptions of features and changes -- should be included in the primary documentation. Which, of course, is kept up to date and needs no errata.
For other thoughts on effective read me files, particularly for shareware software, see Tonya Engst's Read Me Rules series in TidBITs. If you're authoring for Mac OS X, also see Better Read Me Files with TextEdit.