Add the installation/removal instructions for the timeshift Arch package (#220)

Author: Antiz96

README.md

@@ -168,6 +168,12 @@ sudo dnf update
 sudo dnf install timeshift
 ```
 
+#### Arch
+
+```sh
+sudo pacman -S timeshift
+```
+
 ## Removal
 
 Run the following command in a terminal window:  
@@ -178,6 +184,10 @@ or
 
     sudo dnf remove timeshift
 
+or
+
+    sudo pacman -R timeshift
+
 depending in your package management system.
 
 Remember to delete all snapshots before un-installing. Otherwise the snapshots continue to occupy space on your system.  To delete all snapshots, run the application, select all snapshots from the list (CTRL+A) and click the _Delete_ button on the toolbar. This will delete all snapshots and remove the _/timeshift_ folder in the root directory.