Adding a Quick Tour section to the query builder chapter

I figured there where plenty people that did not understand the philosophy
of Query objects to the point that they had troubles getting the first
result of the result set.
Fixed typo
Fixed another typo
Fixed another issue found in review
Merge pull request #1569 from cakephp/3.0-query-quick-tour

Adding a Quick Tour section to the query builder chapter
Fixes in Query object docs
Merge pull request #1570 from bcrowe/3.0-query-quick-tour

3.0 - Fixes in Query object docs