Update spec/Section 2 -- Source Schema.md

Co-authored-by: Glen <[email protected]>

spec/Section 2 -- Source Schema.md

@@ -238,7 +238,7 @@ type Query {
 }
 ```
 
-The above example declares the key field `sku` to be inaccessible through from
+The above example declares the key field `sku` to be inaccessible from
 the composite schema. However, type system members marked as inaccessible can
 still be used within the composite execution schema to fulfill requirements or
 lookups.