Update clone.txt
DOCS-4506: clarify field/key
improvements to set reference
improvements to findAndModify command ref
edits with sam's fb
DOCS-4398: clarifies authenticationDatabase description

- --authenticationDatabase is required for mongotop and mongostat
  when connecting to a mongod or mongos that uses auth
DOCS-3400: further clarifies default for non-tools
DOCS-3400: clarifies default for mongo