You must have Fugitive (http://www.vim.org/scripts/script.php?script_id=2975)
pluging installed in your Vim editor. Just copy plugin/gerrvim.vim file
to ~/.vim/plugin. Optionally copy documentation from doc/gerrvim.txt
to ~/.vim/doc.

gerrvim2json.pl converter requires Perl interpreter and JSON
(https://metacpan.org/pod/JSON) library. No specific installation for it
required -- just call it from any place.