Copy edits to the release notes.

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-2746 update configuration example

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-2706 add arbiter config options

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-3063 convert homebrew install to steps format

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-3063: tweaking wording
DOCS-2868 add 'deprecated' flag to lockType