Add openSUSE prerequisite instructions

These instructions were tested on openSUSE Tumbleweed and openSUSE Leap
15.1. There are some modules left that are not documented yet, but this
already improves the sitution for common openSUSE users.

modules/lang/elixir/README.org

@@ -11,6 +11,7 @@
     - [[#with-asdf][With ~asdf~]]
     - [[#arch-linux][Arch Linux]]
     - [[#gentoo-linux][Gentoo Linux]]
+    - [[#opensuse][openSUSE]]
 - [[#features][Features]]
 
 * Description
@@ -47,6 +48,11 @@ sudo pacman -S elixir
 #+BEGIN_SRC sh :dir /sudo::
 sudo emerge -v dev-lang/elixir
 #+END_SRC
+
+*** openSUSE
+#+BEGIN_SRC sh :dir /sudo::
+sudo zypper install elixir
+#+END_SRC
 * Features
 - Code completion (~:completion company~)
 - Documentation lookup (~:tools lookup~)