If you want help finding errors in documentation, or help improving the quality of writing, or if you are not a native speaker of English and want help producing good English documentation, you can use the GNU proofreaders mailing list: firstname.lastname@example.org.
But be careful when you use the list, because there are over 200 people on it. If you simply ask everyone on the list to read your work, there will probably be tremendous duplication of effort by the proofreaders, and you will probably get the same errors reported 100 times. This must be avoided.
Also, the people on the list do not want to get a large amount of mail from it. So do not ever ask people on the list to send mail to the list!
Here are a few methods that seem reasonable to use:
Be sure to specify the random choice procedure; otherwise people will probably use a mental procedure that is not really random, such as “pick a part near the middle”, and you will not get even coverage.
You can either divide up the work physically, into 20 separate files, or describe a virtual division, such as by sections (if your work has approximately 20 sections). If you do the latter, be sure to be precise about it—for example, do you want the material before the first section heading to count as a section, or not?