Add docs about BPF_HASH_OF_MAPS
Add docs about BPF_HASH_OF_MAPS

brendangregg/bcc,brendangregg/bcc,iovisor/bcc,iovisor/bcc,brendangregg/bcc,iovisor/bcc,iovisor/bcc,brendangregg/bcc,iovisor/bcc,brendangregg/bcc