This is very cool software for people who always need something to read when they think they are idle. You can store variety of documents, PDFs etc and view it in this software. One differentiating thing I found with this software is that it opens documents in your internet browser so you can rotate your phone horizontally and readability improves automatically.
To install Docs, you can search Docs either in Cydia or in Installer, whichever you like. And then install it.