docs: Adds context computation documentation

Author: NeedleInAJayStack

README.md

@@ -98,6 +98,21 @@ Response:
 
 See the `graphql` function documentation for advanced configuration options.
 
+### Computing GraphQL Context
+
+The required closure in the `graphql` function is used to compute the `GraphQLContext` object, which is injected into each GraphQL resolver. The `inputs` argument passes in data from the request so that the Context can be created dynamically:
+
+```swift
+router.graphql(schema: schema) { inputs in
+    return GraphQLContext(
+        userID: inputs.hummingbirdContext.userID,
+        logger: inputs.hummingbirdContext.logger,
+        debug: inputs.hummingbirdRequest.headers[.init("debug")!] != nil,
+        operationName: inputs.graphQLRequest.operationName
+    )
+}
+```
+
 ### WebSockets
 
 Subscription support via WebSockets can be enabled by calling the `graphqlWebSocket` function on a `Router` whose context conforms to `WebSocketRequestContext`, from the `HummingbirdWebSocket` package: