Added Patch

spec/Section 2 -- Source Schema.md

@@ -135,6 +135,32 @@ type Repository @key(fields: "id organization { id }") {
 }
 ```
 
+### @patch
+
+```graphql
+directive @patch on FIELD_DEFINITION
+```
+
+The `@patch` directive is used within a _source schema_ to specify object fields
+that can be used by the _distributed GraphQL executor_ to resolve additional
+data for an entity rather than fetching the entity itself. A patch resolver
+result does noth mean that the actual entity exists.
+
+```graphql example
+type Query {
+  personById(id: ID!): Person @patch
+  personByName(name: String!): Person @patch
+}
+
+type Person @key(fields "id") @key(fields "name") {
+  id: ID!
+  name: String!
+}
+```
+
+Patch resolve as oposed to lookup fields will be omitted from the _composite
+schema_ but will be referenced within the _composite execution schema_.
+
 ### @is
 
 ```graphql