CVE-2018-4407 PoC docs: Advice to use linux capabilities instead of running with full root privileges

[altmas5]

Added a small advice at the end of README for giving the CAP_NET_RAW capability required for opening a raw socket instead of running the binaries with sudo (temporary root privileges).

Once the capability is granted any user can run direct_attack or crash_all with their privileges.

Let's break up with the root model :)

[kevinbackhouse]

Thanks!

[jmdh]

Hi @altmas5 and thanks again for this contribution! Owing to an oversight on our part, the Semmle CLA had not been added to this repository at the time of your contribution. So that we can keep your contribution, we would appreciate it if you could sign our CLA, here https://cla.semmle.com/Semmle/SecurityExploits?pullRequest=3

Thanks again.