DOCS-3985 - Providing warnings re: supported versions of OS'es.

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-3985 - capitalization harmonization

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-3985: style edits
DOCS-3883 - details about user privileges/roles necessary to use mongostat and monogotop

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-3883: style and organization