Re arrange docs for Ops (#6031)

* try re arranging docs

* rewrite docs a bit

* Apply suggestions from code review
Co-authored-by: Vasilis Vryniotis <datumbox@users.noreply.github.com>
Co-authored-by: Vasilis Vryniotis <datumbox@users.noreply.github.com>

docs/source/ops.rst

@@ -5,54 +5,97 @@ Operators
 
 .. currentmodule:: torchvision.ops
 
-:mod:`torchvision.ops` implements operators that are specific for Computer Vision.
+:mod:`torchvision.ops` implements operators, losses and layers that are specific for Computer Vision.
 
 .. note::
   All operators have native support for TorchScript.
 
+
+Detection and Segmentation Operators
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The below operators perform pre-processing as well as post-processing required in object detection and segmentation models.
+
 .. autosummary::
     :toctree: generated/
     :template: function.rst
 
     batched_nms
+    masks_to_boxes
+    nms
+    roi_align
+    roi_pool
+    ps_roi_align
+    ps_roi_pool
+
+.. autosummary::
+    :toctree: generated/
+    :template: class.rst
+
+    FeaturePyramidNetwork
+    MultiScaleRoIAlign
+    RoIAlign
+    RoIPool
+    PSRoIAlign
+    PSRoIPool
+
+
+Box Operators
+~~~~~~~~~~~~~
+
+These utility functions perform various operations on bounding boxes.
+
+.. autosummary::
+    :toctree: generated/
+    :template: function.rst
+
     box_area
     box_convert
     box_iou
     clip_boxes_to_image
     complete_box_iou
-    complete_box_iou_loss
-    deform_conv2d
-    drop_block2d
-    drop_block3d
-    generalized_box_iou
-    generalized_box_iou_loss
     distance_box_iou
-    distance_box_iou_loss
-    masks_to_boxes
-    nms
-    ps_roi_align
-    ps_roi_pool
+    generalized_box_iou
     remove_small_boxes
-    roi_align
-    roi_pool
+
+Losses
+~~~~~~
+
+The following vision-specific loss functions are implemented:
+
+.. autosummary::
+    :toctree: generated/
+    :template: function.rst
+
+    complete_box_iou_loss
+    distance_box_iou_loss
+    generalized_box_iou_loss
     sigmoid_focal_loss
-    stochastic_depth
+
+
+Layers
+~~~~~~
+
+TorchVision provides commonly used building blocks as layers:
 
 .. autosummary::
     :toctree: generated/
     :template: class.rst
 
-    RoIAlign
-    PSRoIAlign
-    RoIPool
-    PSRoIPool
-    DeformConv2d
-    MultiScaleRoIAlign
-    FeaturePyramidNetwork
-    StochasticDepth
-    FrozenBatchNorm2d
     Conv2dNormActivation
     Conv3dNormActivation
-    SqueezeExcitation
+    DeformConv2d
     DropBlock2d
     DropBlock3d
+    FrozenBatchNorm2d
+    SqueezeExcitation
+    StochasticDepth
+
+.. autosummary::
+    :toctree: generated/
+    :template: function.rst
+
+    deform_conv2d
+    drop_block2d
+    drop_block3d
+    stochastic_depth