Minor fixes for Catalog customization chapter (#1)

Author: snowcore

7. Customizing the Catalog/1. Demonstrate ability to use products and product types.md

@@ -31,13 +31,13 @@ Product type model - [Magento\Catalog\Model\Product\Type\AbstractType](https://g
 - [*bundle*](https://github.com/magento/magento2/blob/2.2-develop/app/code/Magento/Bundle/Model/Product/Type.php)
 
     Add 1 composite product, consisting of many selected variations, options independent.
-    Sku dynamic/fixed, weight dynamic/fixed, price dynamic/fixed. Each qty x total qty.
+    SKU dynamic/fixed, weight dynamic/fixed, price dynamic/fixed. Each qty x total qty.
     Inventory is tracked separately for each child.
 
 - *gift card (Commerce edition)*
 
     Like downloadable, purchase gift card code instead of link.
-    Can be virtual/physica/both. Thus can be shipped.
+    Can be virtual/physical/both. Thus can be shipped.
 
 ## product_types.xml - maximum configuration:
 ```xml
@@ -66,7 +66,7 @@ Product type model - [Magento\Catalog\Model\Product\Type\AbstractType](https://g
 ### How would you obtain a product of a specific type?
 
 Product type code is stored in catalog_product_entity.type_id. Thus, we can use collection:
-`productCollection->addFieldToFilter('type_id', 'simple');`
+`$productCollection->addFieldToFilter('type_id', 'simple');`
 
 ### What tools (in general) does a product type model provide?