Merge pull request #1510 from Sparkenstein/master

Added polar bookshelf in ebooks management section

README.md

@@ -586,6 +586,7 @@ _Personal e-book management software._
   - [BicBucStriim](http://projekte.textmulch.de/bicbucstriim/) - Provides web-based access to your Calibre Library's e-book collection. ([Source Code](https://github.com/rvolz/BicBucStriim)) `MIT` `PHP`
   - [Calibre Web](https://github.com/janeczku/calibre-web) - Web app providing a clean interface for browsing, reading and downloading eBooks using an existing Calibre database. ([Source Code](https://github.com/janeczku/calibre-web)) `GPL-3.0` `Python`
   - [COPS](https://blog.slucas.fr/en/oss/calibre-opds-php-server) - Lightweight e-book server alternative to Calibre content server or [Calibre2OPDS](https://calibre2opds.com/2011/11/03/new-site-for-calibre2opds/). ([Demo](http://cops-demo.slucas.fr/index.php), [Source Code](https://github.com/seblucas/cops)) `GPL-2.0` `PHP`
+  - [Polar Bookshelf](https://getpolarized.io/) - Polar is a personal knowledge repository for PDF and web content supporting incremental reading and document annotation. ([Source Code](https://github.com/burtonator/polar-bookshelf)) `GPL` `Javascript` 
 
 _Enterprise-class library management software._