Update README with nfsd collector. (#826)
Update README with nfsd collector. (#826)

Add missing documentation about the `nfsd` collector.
prometheus/node_exporter,derekmarcotte/node_exporter,siavashs/node_exporter,siavashs/node_exporter,siavashs/node_exporter,siavashs/node_exporter,derekmarcotte/node_exporter,prometheus/node_exporter,prometheus/node_exporter,derekmarcotte/node_exporter,derekmarcotte/node_exporter