Add Flatpak badge to Linux install options

Included a Flathub badge in the Linux installation table to indicate Flatpak bundle availability.

README.md

@@ -87,6 +87,7 @@ ytsage
 | ![Linux DEB](https://img.shields.io/badge/Linux-DEB-FCC624?style=for-the-badge&logo=linux&logoColor=black) | Debian package |
 | ![Linux AppImage](https://img.shields.io/badge/Linux-AppImage-FCC624?style=for-the-badge&logo=linux&logoColor=black) | AppImage, portable |
 | ![Linux RPM](https://img.shields.io/badge/Linux-RPM-FCC624?style=for-the-badge&logo=linux&logoColor=black) | RPM package |
+| ![Flathub](https://img.shields.io/badge/Linux-Flatpak-FCC624?style=for-the-badge&logo=flathub&logoColor=black) | Flatpak Bundle |
 
 #### 🍎 macOS