src/TableBlueprint.php
public function addIndex(array $columns, array $options = []): self
    {
        return $this->addOperation(
            new Operation\Index\Add($this->table, $columns, $options)
        );
    }
public function addIndex(array $columns, array $options = []): self
    {
        return $this->addOperation(
            new Operation\Index\Add($this->table, $columns, $options)
        );
    }
Example:
$table->addIndex(['email'], ['unique' => true]);

@param array $columns
@param array $options
@return TableBlueprint