message: Document record field shorthands in the reference
diff: @@ -818,6 +818,18 @@ let origin : Point = {
  };
  ```
  +The right hand side of the field definition can be omitted if it is a variable with
  +the same name as the field. For example:
  +
  +```fathom
  +let Point = { x : U32, y : U32 };
  +
  +let x : U32 = 0;
  +let y : U32 = 0;
  +
  +let origin : Point = { x, y };
  +```
  +
  When checking dependent record types, the values assigned to field expressions
  will substituted into the types of subsequent fields. For example:
  