Confusing README related to KERNEL_SRC

[jbjorkang]

I attempted to build ovpn-dco with a kernel different to that running on my system (6.3.0).

The README states:

If you want to build ovpn-dco against a kernel different from the one
running on the host, run:
$ make KERNEL_SRC=/path/to/the/kernel/tree

However it omits to mention that it should be a built kernel tree, rather than just the source code.

Suggestion:

If you want to build ovpn-dco against a kernel different from the one running on the host, ensure you have a built Linux kernel checked out at the desired version:
$ git clone https://github.com/OpenVPN/ovpn-dco.git
$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
$ cd linux/
$ git checkout ...
$ make
$ cd ../ovpn-dco/
$ make KERNEL_SRC=../linux/