MB-5307: added documentation for ns_server supervisor hierarchy
MB-5307: added documentation for ns_server supervisor hierarchy

Change-Id: Ibf4c661e07e2ed46e158618de8c10627dec75ab0
Reviewed-on: http://review.couchbase.org/16208
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

membase/ns_server,vzasade/ns_server,vzasade/ns_server,pavel-blagodov/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,ceejatec/ns_server,ceejatec/ns_server,vzasade/ns_server,mschoch/ns_server,mschoch/ns_server,nimishzynga/ns_server,pavel-blagodov/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,pavel-blagodov/ns_server,t3rm1n4l/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,membase/ns_server,nimishzynga/ns_server,daverigby/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,daverigby/ns_server,membase/ns_server,membase/ns_server,daverigby/ns_server,t3rm1n4l/ns_server,vzasade/ns_server,nimishzynga/ns_server,mschoch/ns_server,daverigby/ns_server,ceejatec/ns_server,nimishzynga/ns_server,membase/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,mschoch/ns_server,nimishzynga/ns_server,daverigby/ns_server