README: update instructions for Arch

We have a meta package `base-devel` that defines the basic tools to
build Arch Linux packages. Just install that and its dependencies,
and `ncurses`.

Also add `--needed` to skip packages that are installed already.

Author: eworm-de

README.md

@@ -86,7 +86,7 @@ sudo zypper install ncurses-devel ncurses-devel-static automake autoconf gcc mak
 
 **Archlinux/Manjaro**
 ~~~ shell
-sudo pacman -S ncurses automake autoconf gcc
+sudo pacman -S --needed base-devel ncurses
 ~~~
 
 **macOS**