correcting secondaryThrottle explanation

it only added w:2 for "every" document, we wait for majority during critical section even if secondaryThrottle is false.

Signed-off-by: Sam Kleinman <samk@10gen.com>
Explicitly label findAndModify example as Update and return

Many people confused into thinking findAndModify is needed to update a document atomically.  Clarifying that it "updates and returns".

Signed-off-by: Sam Kleinman <samk@10gen.com>
grammar

Signed-off-by: Sam Kleinman <samk@10gen.com>