docs: use ./scripts/config tool for kernel configuration

[Slava0135]

Is your feature request related to a problem? Please describe.
Document about configuring kernel just lists the required configurations, e.g. CONFIG_KCOV=y, however it's not very convenient when there are 10s of them and you need to enable/disable each.

Describe the solution you'd like
Use ./scripts/config in docs, e.g. ./scripts/config -e KCOV so you can just copy code snippet in shell and enable multiple options at once, like this:

./scripts/config -e NAMESPACES -e UTS_NS -e IPC_NS -e PID_NS -e NET_NS -e CGROUP_PIDS -e MEMCG

Additional context