Add K2pdfopt

K2pdfopt optimizes PDF/DJVU files for mobile e-readers (e.g. the Kindle)
and smartphones. It works well on multi-column PDF/DJVU files and can
re-flow text even on scanned PDF files. It can also be used as a general
PDF copying/cropping/re-sizing/OCR-ing manipulation tool. It can
generate native or bitmapped PDF output, with an optional OCR layer.

README.md

@@ -335,6 +335,7 @@
 - [![Open-Source Software][OSS Icon]](https://github.com/geometer/FBReader) [FBReader](https://fbreader.org/content/fbreader-beta-linux-desktop) - One of the most popular eReader apps.
 - [Foxit](https://www.foxitsoftware.com/pdf-reader/) - Foxit Reader 8.0—Award-winning PDF Reader.
 - [![Open-Source Software][OSS Icon]](https://github.com/martahilmar/gnome-books) [Gnome Books](https://github.com/martahilmar/gnome-books) - GNOME Books is application for listing, searching and reading eBooks.
+- [![Open-Source Software][OSS Icon]](https://www.willus.com/k2pdfopt/src) [K2pdfopt](https://www.willus.com/k2pdfopt) - K2pdfopt optimizes PDF/DJVU files for mobile e-readers (e.g. the Kindle) and smartphones.
 - [![Open-Source Software][OSS Icon]](http://repo.or.cz/w/llpp.git) [llpp](https://wiki.archlinux.org/index.php/Llpp) - A lightweight, fast, customizable and featureful PDF, EPUB, XPS and CBZ viewer with vi-like keybindings based on MuPDF.
 - [Lucidor](https://www.lucidor.org/lucidor/) - Lucidor is a computer program for reading and handling e-books. Lucidor supports e-books in the EPUB file format, and catalogs in the OPDS format.
 - [MasterPDF editor](https://code-industry.net/free-pdf-editor/) - Master PDF Editor a convenient and smart PDF editor for Linux.