add description for ebook category

- https://github.com/awesome-selfhosted/awesome-selfhosted/issues/2984

README.md

@@ -755,6 +755,8 @@ A [document management system](https://en.wikipedia.org/wiki/Document_management
 
 **[`^        back to top        ^`](#)**
 
+[Ebook](https://en.wikipedia.org/wiki/Ebook) library management software.
+
 - [BicBucStriim](https://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. `GPL-3.0` `Python`
 - [Calibre](https://calibre-ebook.com/) - E-book library manager that can view, convert, and catalog e-books in most of the major e-book formats and provides a built-in Web server for remote clients. ([Demo](https://calibre-ebook.com/demo), [Source Code](https://launchpad.net/calibre)) `GPL-3.0` `Python`