Add Arch / Manjaro dependencies (#275)

Author: wyhaya

docs/linux_dependencies.md

@@ -5,7 +5,16 @@ This page lists the required dependencies to build a Bevy project on your Linux
 If you don't see your distro present in the list, feel free to add the instructions in this document.
 
 ## Ubuntu 20.04
-`sudo apt-get install libx11-dev libasound2-dev`
+```bash
+sudo apt-get install libx11-dev libasound2-dev
+```
 
 ## Fedora 32
-`sudo dnf install gcc-c++ libX11-devel alsa-lib-devel`
+```bash
+sudo dnf install gcc-c++ libX11-devel alsa-lib-devel
+```
+
+## Arch / Manjaro
+```bash
+sudo pacman -S libx11 pkgconf alsa-lib
+```