Include more directive locations

Author: leebyron

spec/Section 2 -- Language.md

@@ -1169,6 +1169,27 @@ Since the validation of a GraphQL document includes ensuring that any directives
 used are defined and used correctly, defining a directive allows for a validator
 to be aware of all possible validation rules.
 
+As part of validation, directives are only allowed to be used in locations
+that are explicitly declared. Directive locations must be one of:
+
+ * `QUERY`
+ * `MUTATION`
+ * `FIELD`
+ * `FRAGMENT_DEFINITION`
+ * `FRAGMENT_SPREAD`
+ * `INLINE_FRAGMENT`
+ * `SCHEMA`
+ * `SCALAR`
+ * `OBJECT`
+ * `FIELD_DEFINITION`
+ * `ARGUMENT_DEFINITION`
+ * `INTERFACE`
+ * `UNION`
+ * `ENUM`
+ * `ENUM_VALUE`
+ * `INPUT_OBJECT`
+ * `INPUT_FIELD_DEFINITION`
+
 In this example, a directive is defined which can be used to annotate a
 fragment definition:
 
@@ -1179,3 +1200,15 @@ fragment SomeFragment on SomeType @someAnnotation(arg: "abc") {
   someField
 }
 ```
+
+Directives can also be used to annotate the schema language itself:
+
+```
+directive @some(thing: Int) on FIELD_DEFINITION | ARGUMENT_DEFINITION
+
+type SomeType {
+  field(
+    arg: Int @some(thing: 1)
+  ): String @some(thing: 2)
+}
+```

spec/Section 4 -- Introspection.md

@@ -198,6 +198,17 @@ enum __DirectiveLocation {
   FRAGMENT_DEFINITION
   FRAGMENT_SPREAD
   INLINE_FRAGMENT
+  SCHEMA
+  SCALAR
+  OBJECT
+  FIELD_DEFINITION
+  ARGUMENT_DEFINITION
+  INTERFACE
+  UNION
+  ENUM
+  ENUM_VALUE
+  INPUT_OBJECT
+  INPUT_FIELD_DEFINITION
 }
 ```