Update INSTALLATION.md for Arch Linux

- Partial upgrades are not recommended/supported
- Remove dependencies that are pulled in by plasma-framework
- Add python, build fails without python (or python2) installed

INSTALLATION.md

@@ -29,10 +29,8 @@ sudo apt install cmake extra-cmake-modules qtdeclarative5-dev libqt5x11extras5-d
 ### Arch Linux
 
 ```
-sudo pacman -Syy
-sudo pacman -S cmake extra-cmake-modules
-sudo pacman -S qt5-base qt5-declarative qt5-x11extras
-sudo pacman -S kiconthemes kdbusaddons kxmlgui kdeclarative plasma-framework plasma-desktop
+sudo pacman -Syu
+sudo pacman -S cmake extra-cmake-modules python plasma-framework plasma-desktop
 ```
 
 ### Building and Installing