Document about latency histogram

[iyangsj]

Discussed in https://github.com/bfenetworks/bfe/discussions/844

^{Originally posted by **lf2186** September 24, 2021} hi， https://www.bfe-networks.net/zh_cn/monitor/latency/ $ curl -s 'http://localhost:8421/monitor/proxy_handshake_delay?format=prometheus' # TYPE proxy_handshake_delay_Past histogram proxy_handshake_delay_Past_bucket{le="1000"} 8065 proxy_handshake_delay_Past_bucket{le="2000"} 9924 proxy_handshake_delay_Past_bucket{le="3000"} 10278 proxy_handshake_delay_Past_bucket{le="4000"} 10529 proxy_handshake_delay_Past_bucket{le="5000"} 10683 proxy_handshake_delay_Past_bucket{le="6000"} 10785 proxy_handshake_delay_Past_bucket{le="7000"} 10859 proxy_handshake_delay_Past_bucket{le="8000"} 10934 proxy_handshake_delay_Past_bucket{le="9000"} 10982 proxy_handshake_delay_Past_bucket{le="10000"} 11026 proxy_handshake_delay_Past_bucket{le="+Inf"} 11466 proxy_handshake_delay_Past_sum 3160545584 proxy_handshake_delay_Past_count 11466 请问什么时候，可以补充一下这些key的详细说明文档，包括key含义 和 时间粒度等等

[clarinette9]

resolved by pull request #857