How to create Catalog attribute in Magento 2 Using Upgrade Script

First You need to increase version of your file under etc/module.xml.Suppose your version is 1.0.0 then increased it by 1.0.1

Now create UpgradeData.php under Setup folder.

    <?php 
    namespace WilliamsCommerce\OrderBy\Setup;
    use Magento\Framework\Setup\UpgradeDataInterface;
    use Magento\Eav\Setup\EavSetup;
    use Magento\Eav\Setup\EavSetupFactory;
    use Magento\Framework\Setup\ModuleContextInterface;
    use Magento\Framework\Setup\ModuleDataSetupInterface;
    use Magento\Catalog\Setup\CategorySetupFactory;
    use Magento\Eav\Model\Entity\Attribute\SetFactory as AttributeSetFactory;

    class UpgradeData implements UpgradeDataInterface
    {
       private $eavSetupFactory;
       private $attributeSetFactory;
       private $attributeSet;
       private $categorySetupFactory;

       public function __construct(EavSetupFactory $eavSetupFactory, AttributeSetFactory $attributeSetFactory, CategorySetupFactory $categorySetupFactory )
           {
               $this->eavSetupFactory = $eavSetupFactory;
               $this->attributeSetFactory = $attributeSetFactory;
               $this->categorySetupFactory = $categorySetupFactory;
           }

       public function upgrade(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
       {    // TO CREATE PRODUCT ATTRIBUTE
           if (version_compare($context->getVersion(), '1.0.1') < 0) {
           $setup->startSetup();
           $eavSetup = $this->eavSetupFactory->create(['setup' => $setup]);
               $eavSetup->addAttribute(
                       \Magento\Catalog\Model\Product::ENTITY,
                   'feature_1',
                   [
                        'group' => 'Product Details',
                        'type'  => 'varchar',
                        'label' => 'Feature 1',
                        'input' => 'text',
                        'frontend' => '',
                        'required' => false,
                        'global' => 1,
                        'visible' => true,
                        'required' => false,
                        'user_defined' => true,
                        'default' => null,
                        'searchable' => false,
                        'filterable' => false,
                        'comparable' => false,
                        'visible_on_front' => true,
                        'used_in_product_listing' => true,
                        'unique' => false,
                        'apply_to' => '',
                        'note' => 'Feature 1'
               ]
           );  

           $setup->endSetup();
       }
       }
    } 
?>