kpatch: look for core module in git dir

Allow "kpatch load" to find the core module when kpatch is run directly
from the git tree.  This gives the user the option to use the kpatch
utility directly without having to do a "make install".
readme: recommend use of the kpatch utility

The kpatch utility is now user friendly enough that it can be used
instead of direct insmods.  We should encourage people to use it, since
we will soon be adding user space functionality above and beyond
insmod/rmmod when loading and unloading.
Merge pull request #134 from jpoimboe/find-core-module-git-tree

kpatch: look for core module in git dir