To install the class, simply copy-paste the contents of the source folder
into the folder where your .tex is. Otherwise, if you have cloned
this repo, you can create a symbolic link to it inside your local texmf folder
where LaTeX finds local packages :
mkdir ~/texmf/tex/latex
ln -s <path to your crclart clone>/source ~/texmf/tex/latex/crclart
See the example in the template folder to see how you can use the class to
write your article following the CRCL journal submission
guidelines.