Fix broken links for Arch Linux in the README

Arch Linux has recently migrated its packages to Git (see https://archlinux.org/news/git-migration-completed/). As a result, the package 'gfold' has been moved to the Extra repository instead of the Community repository. This commit fixes a bug in the README where the badge about Arch Linux was broken along with the corresponding links.

README.md

@@ -112,9 +112,9 @@ _Note:_ the tap may not work with [Linuxbrew](https://docs.brew.sh/Homebrew-on-L
 
 ### Arch Linux
 
-[![arch linux](https://img.shields.io/archlinux/v/community/x86_64/gfold?logo=archlinux&logoColor=white&style=flat-square&color=blue)](https://archlinux.org/packages/community/x86_64/gfold/)
+[![arch linux](https://img.shields.io/archlinux/v/extra/x86_64/gfold?logo=archlinux&logoColor=white&style=flat-square&color=blue)](https://archlinux.org/packages/extra/x86_64/gfold/)
 
-You can use [pacman](https://wiki.archlinux.org/title/Pacman) to install `gfold` from the [community repository](https://archlinux.org/packages/community/x86_64/gfold/).
+You can use [pacman](https://wiki.archlinux.org/title/Pacman) to install `gfold` from the [Extra repository](https://archlinux.org/packages/extra/x86_64/gfold/).
 
 ```shell
 pacman -S gfold