Richard Stallman, founder of the GNU project and the term 'copyleft' wrote about Free Documentation in his book "Free Software, Free Society : Selected Essays of Richard Stallman".
"The biggest deficiency in our free operating systems is not in the software‚Äîit is the lack of good free manuals that we can include in our systems. Documentation is an essential part of any software package; when an important free software package does not come with a good free manual, that is a major gap. We have many such gaps today. "
"Free documentation, like free software, is a matter of freedom, not price. The criterion for a free manual is pretty much the same as for free software: it is a matter of giving all users certain freedoms. Redistribution (including commercial sale) must be permitted, on-line and on paper, so that the manual can accompany every copy of the program. "
FLOSS Manuals is a site dedicated to providing free and open source, FLOSS manuals on a variety of technical topics such as audio editing, VOIP, video editing, streaming, free culture, audio editing, media players, and more. visit their site to read the manuals : http://en.flossmanuals.net/