Vim must have been compiled with +clientserver
Help is here
:h clientserver
Start Vim in server mode
vim --servername vim
Check my new server
vim --serverlist
Open a file in a running Vim
vim --remote {file}
NB : By default, Vim use the program name as servername
Open a file in a split
vim --remote +sp d
Refresh Vim
vim --remote-send ":checkt<CR>"
TODO : use git hook