Add RHEL/Centos docs, move to wpa_supplicant v2.0 and fix /etc bug

Essentially a one-liner, and entirely self-explanatory doc update for Centos deps. vim-common doesn't strike me as the sanest packaging of /usr/bin/xxd but that's where you find it on RHEL...

Addresses Issue #4 with a clean copy to reset for the next make, rather than a series of moves

Migrated to buildroot-internal build of wpa_supplicant v2.0 with wpa_cli as an evolutionary step for issue #1