document struct support

Author: Christopher Rowley

docs/src/juliacall-reference.md

@@ -202,8 +202,9 @@ jl.Vector[jl.Int]()
 ```
 
 Some Julia types can be converted to corresponding numpy dtypes like `numpy.dtype(jl.Int)`.
-Currently supports these primitive types: `Bool`, `IntXX`, `UIntXX`, `FloatXX`,
-`ComplexFXX`, `NumpyDates.InlineDateTime64{unit}` and `NumpyDates.InlineTimeDelta64{unit}`.
+Supports primitive types: `Bool`, `IntXX`, `UIntXX`, `FloatXX`, `ComplexFXX`,
+`NumpyDates.InlineDateTime64{unit}` and `NumpyDates.InlineTimeDelta64{unit}`. Also
+supports tuples, named tuples and structs of these.
 `````
 
 `````@customdoc