Update Scopes and Collections page to make the content clear to first time Couchbase users

(https://docs.couchbase.com/server/current/learn/data/scopes-and-collections.html)

The Scopes and Collections page assumes the end user is familiar with the Couchbase concepts. 

For instance - the first line starts with "A collection is a data container, defined on Couchbase Server, within a bucket whose type is either Couchbase or Ephemeral. " 

A new user may not be aware of the bucket type Couchbase or Ephemeral.