This simple contribution layer is an example. It installs around 100 themes
for Emacs. You can try them easily by invoking helm-themes with: SPC T s.
You can see samples of all included themes in this theme gallery from Rob Merrell.
To use this configuration layer, add it to your ~/.spacemacs. You will need to
add themes-megapack to the existing dotspacemacs-configuration-layers list in this
file.