I download lots of software and, man, some of them are just really frustrating. There's 0 documentation on how to install or use the software and I have to spend tons of time Googling and reading lots of text.

Unless your software is an .exe or an .msi which creates a ready to use program out of the box, PLEASE PLEASE
spend a few minutes typing a quick docs file and include it in your archive file. A file like readme.txt. If anything, put your url in that file so in the future I can know where to to go to look for more information. I have some modules and I have no idea where I got them from. I have to dig for keywords from the files  and Google them. In your site PLEASE include some quick start or quick installation docs. It doesn't have to be pretty or have any formatting. Just whip one up quickly.

It seems developers just zip their folders or create a module without any documentation. if you are a developer and you spent tens of hours developing a module, why can't you spend like 15 minutes typing something up and include it in your zip file!? Open up an editor and just type and type. if you're too busy, forget about cleaning it up. It seems this what discourages developers from producing any kinds of docs.

If your module expects free form text (not a checkbox or radio button or a dropdown list) from the user in your settings, you should provide examples of what the field is expecting. If I enter something that didn't validate or is in wrong format, don't just say it's bad data or it's wrong. Tell me exactly why it's bad and what you are expecting. Don't throw an exception at my face. Make your error message as clear as possible. I don't care if they are too verbose. Don't make me think.

It seems a lot of developers think the whole world are developers like them and we can read their minds and understand their apps by just looking at them. Put yourself in the shoes of a non technical user and pretend you know nothing about the app infront of you. if anything might look confusing or not clear to the user, you should add tips, hints, examples & help sections. if you're putting a "?" icon next to a field, don't repeat what the label says. Bring up a tip window which clearly explains what it is and what it's NOT and show some examples.
If you are creating a free module and don't want to invest time in this, again, just put everything in a text file and just type what's in your mind. You will be helping everyone including yourself by not getting support  issues by email, forums and by not frustrating prospective customers.

When I download module, it's in a zip file. I expect some kind of quick docs in the zip file. It's for human consumption, not for DNN use and not part of the manifest.

Use long file names to your advantage. How about something like: MyFormModule_for_DNN5_only.zip? If you want to go crazy do this: MyFormModule_for_DNN5_only (use file MyFormModule_for_versions_below DNN5_only.zip).zip. I bet no one will be confused then, will they? And it never hurts to do something like that.  I am surprised a lot of people still try to cram file names into 8 characters only. We left Win3.1 very long time!

As for putting docs inside the zip file. It should be a good practice specially when no docs are available on the website either. What if I am on the plane in a long flight with no web access? An included documentation, which most people don't like to read, would help people with the software AND help kill boring time during the flight!
Personally it annoys me when a software's help is an online version *only*. Not a good idea. At least do it like Visual Studio where you give the option of one or the other or both.