As I just wrote in the unified emulator menu button thread, I don't think developers are keen on creating documentation that will just not be read, instead just answering users' questions as they come up. I think the other way: making manuals for applications makes sense because you never know when or where your users will get stuck in the future, and they might not be able to ask you, or you might not be available.
You could help create manuals or proofread manuals that users create for their favourite applications. That would be a good use of your proofreading abilities.
I offer the PocketSNES, ReGBA and Hocoslamfy manuals as templates:
https://github.com/Nebuleon/PocketSNES/blob/master/data/manual-en.txthttps://github.com/Nebuleon/ReGBA/blob/master/source/opendingux/data/manual-en.txthttps://github.com/Nebuleon/hocoslamfy/blob/master/data/manual-en.txtEmulator port documentation should include at least how to get the emulator's files and directories set up before the first run (in cases like ReGBA which can use a GBA BIOS you provide, or MAME4ALL and FBA which have ROM directories to set up with a certain ROM set), how to set your default game directory and select a ROM, re-enter the menu, exit the emulator, switch games, and explain button bindings and options in decent detail. This would allow a user who forgot all about how he or she set up an emulator, but lost data or something, to set the emulator up again with minimum fuss.
Some game engine ports with copyrighted data files, like eduke32, have a screen in which they tell users what files to put where before aborting if they don't find the files. That's good too, but a manual with button bindings would be even better.