From my experience OSMC (which is based on Debian/Raspbian) is much easier to modify than OpenElec, because all the Debian or Ubuntu based tutorials work, the commands and places where config files are stored are similar etc.
Here is a tutorial which explains how to get into the command line: https://osmc.tv/wiki/general/accessing-the-command-line/
There one can do the steps described here: http://apt.syncthing.net/
If you get an error saying that “curl” or one of the other tools isn’t installed, you can follow this guide to install those first: https://osmc.tv/wiki/general/installing-packages-via-apt/