Update shaping rate help

Repoted by Mr Kentaro Ebisawa.

  http://blog.ebiken.me/vyos-traffic-policy-conf-bitbyte/
  (Japanese page)
  
This help is hard to understand. 

    vyos@vyos# set traffic-policy shaper ICMP-OUTGOING default bandwidth 500Mbps
    Possible completions:
        <number>     Bandwidth in Kbps
        <number>%    Percentage of overall rate (default 100%)
        <number><suffix>
                    Value with scaling suffix (kbit, kbps, ...)

I updated help.

After

    vyos@vyos# set traffic-policy shaper ICMP-OUTGOING default bandwidth 500Mbps
    Possible completions:
       <number>     Bandwidth in Kbps(10^3 bits per second)
       <number>%    Percentage of overall rate (default 100%)
       <number>bit  bit(1), kbit(10^3), mbit(10^6), gbit, tbit
       <number>ibit kibit(1024), mibit(1024^2), gibit(1024^3), tbit(1024^4)
       <number>ibps kibps(1024*8), mibps(1024^2*8), gibps, tibps *Byte/sec*
       <number>bps  bps(8),kbps(8*10^3),mbps(8*10^6), gbps, tbps *Byte/sec*