Add DESTDIR to Makefile for staged installation

[oliryde]

It could be very helpful for packaging k3se.
For now I've made a patch for my packaging script.
I can make a pull request but I would need to adapt my patch to allow for sudo installations to preserve current functionality.

Thanks for making this. It makes k3s very enjoyable and easy to use.

DESTDIR

[nicklasfrahm]

@oliryde Hi, could you provide some guidance as to wheter #22 is good enough. I looked into removing the sudo from the install target, but it is a bit tricky. To find a good solution I would need to know what the regular workflow is. You pointed me to an example the other day.

Is it make followed by sudo make install? Because if that is the case, I am not sure how I feel about removing the sudo because it requires go to be installed for both the current user and root, which is a requirement that I am trying to avoid.

[oliryde]

@nicklasfrahm
If you want to use go in the Makefile to determine which platform and architecture you're on you should probably make it generally available.
Alternatively you can determine at least the architecture with more generally available tools.
Like they've done here