FYI, a Readme.txt already exists. It covers basic info about Dolphin, system requirements, command line usage, and basic plugin and directory information.
It sounds like what you're looking for is an offline manual, which I agree would be helpful. You may want to clarify this, though, as just mentioning "Readme.txt" isn't very descriptive (and, in this case, inaccurate).
One other point: including an offline manual would only be possible if the information/documentation already exists. Currently, there seems to be a dearth of good information about Dolphin configuration, with this page providing the only good (though incomplete) end-user documentation I could find:
http://www.dolphin-emulator.com/configuration-explanation.html
I think step one should be to complete the online documentation (this would be a great way for an experienced Dolphin user to contribute). An easy interim step after that would be to include shortcut links to that documentation with the official packages so that it's easy to find. Finally, once the documentation is complete it can be repackaged in an appropriate format and included with the official pages for offline use.
Certainly doable, and useful. :-)