minor: syntax fix
Update enforce-unique-keys-for-sharded-collections.txt

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

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

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-2471: adding missing word
DOCS-2457: fixing quotes