Edit to docs page on disabling read concern majority

Description

The docs page for disabling read concern majority (https://docs.mongodb.com/v3.6/reference/read-concern-majority/#disable-read-concern-majority) mentions an impact on change streams. I believe it would be worthwhile to mention that customers should review their apps to see if they have implemented read concern majority. Also, I would add that if they either need to use change streams or RCM in their apps, that they should convert the arbiter to a data bearing node

Scope of changes

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)