missing step from installation instructions

I am on ubuntu 18.04 and can-isotp did not work unless I also ran sudo depmod -a after installing.

You may want to add this step to the installation instructions.

It's possible that this was required as a byproduct of https://github.com/hartkopp/can-isotp/issues/7 , which I resolved by generating a signing key. I am not sure if the initial install attempts without the signing key created a messed up install that was not completely overwritten by subsequent install attempts with the signing key present (and I don't know how to uninstall, so I can't try again to be sure!).

Either way, I don't think running sudo depmod -a hurts anything, so why not add it to the install instructions?