text: Title: Add documentation to Camera model about how input angles might be converted
  Body: ## 📚 Documentation
  
  Euler angles in 3D don't uniquely specify a direction. (For example, if I have a vector pointing from the middle of the earth to a point in the equator, if I want to rotate it to point to the north pole, I can rotate it 90º along the longitude axis, or I can rotate it any amount I want along the equator, and then rotate it 90º along *that* longitude.) It turns out that in napari, when we set `viewer.camera.angle`, this gets passed to VisPy, which can normalise the angle after passing through a quaternion, as demonstrated in [this image.sc thread](https://forum.image.sc/t/how-does-napari-handle-3d-camera-angle-setting-unexpected-behavior/97646):
  
  ```python
  import napari
  import numpy as np
  
  viewer = napari.Viewer(ndisplay=3)
  viewer.add_image(np.random.random((5, 5, 5)))
  viewer.camera.angles = (0, 176, -90)
  print(viewer.camera.angles)
  
  napari.run()
  
  print(viewer.camera.angles)
  ```
  
  prints:
  
  ```python
  (0.0, 176.0, -90.0)
  (180.0, 4.000000000000012, 90.0)
  ```
  
  Interestingly, you need both the image layer and the napari.run to see the effect.
  
  There's nothing intrinsically wrong with this, but it can be surprising. Therefore we should probably document it in the Camera docstring, if not in other narrative docs.
  