Make documentation for get_field_def more accurate

Replicates graphql/graphql-js@fb042fc

Author: Cito

src/graphql/execution/execute.py

@@ -1082,11 +1082,11 @@ def get_field_def(
     """Get field definition.
 
     This method looks up the field on the given type definition. It has special casing
-    for the two introspection fields, ``__schema`` and ``__typename``. ``__typename`` is
-    special because it can always be queried as a field, even in situations where no
-    other fields are allowed, like on a Union. ``__schema`` could get automatically
-    added to the query type, but that would require mutating type definitions, which
-    would cause issues.
+    for the three introspection fields, ``__schema``, ``__type`, and ``__typename``.
+    ``__typename`` is special because it can always be queried as a field, even in
+    situations where no other fields are allowed, like on a Union. ``__schema`` and
+    ``__type`` could get automatically added to the query type, but that would require
+    mutating type definitions, which would cause issues.
 
     For internal use only.
     """