Syntax highlighting for Mermaid diagrams.
You'll need Git, because this won't ever appear in Atom's package registry:
# On Unix-like platforms
cd ~/.atom/packages && git clone https://github.com/Alhadis/language-mermaid.git
:: For Windows users
cd %HOMEPATH%\.atom\packages
git clone "https://github.com/Alhadis/language-mermaid.git"