Document performance benchmarks in registry app docs

[jordanpadams]

No description provided.

[tloubrieu-jpl]

On pds-dev-es[123] cluster with 1 milions record, the following request works in

less than 1 second:
GET http://localhost:9200/registry/_doc/urn:nasa:pds:orex.ocams:data_raw:20190702t072824s852_pol_l0pan.fits::1.0

less that 2 seconds:
GET http://localhost:9200/registry/_search
{
"query": {
"match": {
"orex/OCAMS_Instrument_Attributes/orex/cur_motor": "5"
}
}
}