add OSS software polar

which is a reading tool

README.md

@@ -364,6 +364,7 @@
 - [![Open-Source Software][OSS Icon]](https://github.com/KDE/okular) [Okular](https://okular.kde.org/) - Okular is a universal document viewer based developed by KDE. Okular works on multiple platforms, including but not limited to Linux, Windows, Mac OS X, BSD, etc.
 - [![Open-Source Software][OSS Icon]](https://github.com/torakiki/pdfsam) [PDFsam](http://www.pdfsam.org/) - A desktop application to split, extract pages, rotate, mix and merge PDF files.
 - [![Open-Source Software][OSS Icon]](https://download.kde.org/stable/peruse/peruse-1.2.tar.xz.mirrorlist) [Peruse](https://peruse.kde.org/) - A pleasant way to read comic books.
+- [![Open-Source Software][OSS Icon]](https://github.com/burtonator/polar-bookshelf) [Polar](https://getpolarized.io/) - Polar is a personal knowledge repository for PDF and web content supporting incremental reading and document annotation.
 - [![Open-Source Software][OSS Icon]](https://launchpad.net/qpdfview) [qpdf](https://launchpad.net/qpdfview) - qpdfview is a tabbed document viewer.
 - [![Open-Source Software][OSS Icon]](https://github.com/Sigil-Ebook/Sigil) [Sigil](https://github.com/Sigil-Ebook/Sigil) - Sigil is a multi-platform EPUB ebook editor.
 - [![Open-Source Software][OSS Icon]](https://git.pwmt.org/pwmt/zathura.git) [Zathura](https://pwmt.org/projects/zathura/) - Zathura is a highly customizable and functional document viewer.