docs: improve sample code
docs: improve sample code

`$db->table('my_table')->countAllResults()` counts all records in the table.

bcit-ci/CodeIgniter4,bcit-ci/CodeIgniter4,bcit-ci/CodeIgniter4,ytetsuro/CodeIgniter4,ytetsuro/CodeIgniter4,lonnieezell/CodeIgniter4,lonnieezell/CodeIgniter4,ytetsuro/CodeIgniter4,lonnieezell/CodeIgniter4,kenjis/CodeIgniter4,kenjis/CodeIgniter4,bcit-ci/CodeIgniter4,samsonasik/CodeIgniter4,kenjis/CodeIgniter4,kenjis/CodeIgniter4,bcit-ci/CodeIgniter4,kenjis/CodeIgniter4,ytetsuro/CodeIgniter4,lonnieezell/CodeIgniter4,lonnieezell/CodeIgniter4,samsonasik/CodeIgniter4,lonnieezell/CodeIgniter4,samsonasik/CodeIgniter4,samsonasik/CodeIgniter4,ytetsuro/CodeIgniter4,ytetsuro/CodeIgniter4,samsonasik/CodeIgniter4,samsonasik/CodeIgniter4