Improve examples when creating a Dynamic Table Config

When you create a Dynamic Tag, the documentation shows examples using variables such as $table, $dataset and $project.

The following examples exist:

select count(*) from $table;
select count(distinct(account_id)) from $table;
select count(*) > 1 from $table where account_id is null;
select rating from dw-project.quality.scores where table =`$table\' and dataset = `$dataset` and project = `$project`;
- select '30-DAYS';

As you can see, some examples use $table and another uses `$table`, but only the `$table` cases work.

GoogleCloudPlatform / datacatalog-tag-engine