[Docs] add ncnn ops docs samples (#313)

* add ncnn ops docs samples

* link ops to ncnn.md

* fix ncnn.md grammar

* fix grammar typo

docs/en/backends/ncnn.md

@@ -64,6 +64,13 @@ If you haven't installed NCNN in the default path, please add `-Dncnn_DIR` flag
 - This follows the tutorial on [How to convert model](../tutorials/how_to_convert_model.md).
 - The converted model has two files: `.param` and `.bin`, as model structure file and weight file respectively.
 
+
+### List of supported custom ops
+
+| Operator                                                                     |  CPU  |  GPU  | MMDeploy Releases |
+| :--------------------------------------------------------------------------- | :---: | :---: | :---------------- |
+| [Shape](../ops/ncnn.md#shape)                                   |   Y   |   N   | master            |
+
 ### FAQs
 
 1. When running ncnn models for inference with custom ops, it fails and shows the error message like:

docs/en/ops/ncnn.md

@@ -1 +1,40 @@
 ## ncnn Ops
+
+<!-- TOC -->
+
+- [NCNN Ops](#ncnn-ops)
+  - [Shape](#shape)
+    - [Description](#description)
+    - [Parameters](#parameters)
+    - [Inputs](#inputs)
+    - [Outputs](#outputs)
+    - [Type Constraints](#type-constraints)
+
+<!-- TOC -->
+
+### Shape
+
+#### Description
+
+Get the shape of the ncnn blobs.
+
+#### Parameters
+
+Shape has no parameters.
+
+#### Inputs
+
+<dl>
+<dt><tt>inputs[0]</tt>: ncnn.Mat</dt>
+<dd>bottom_blob; An ncnn.Mat. If ncnn version >= 1.0.20201208, the dimension of the bottom_blob should be no more than 4, or the dimension of the bottom_blob should be no more than 3.</dd>
+</dl>
+
+#### Outputs
+<dl>
+<dt><tt>outputs[0]</tt>: T</dt>
+<dd>top_blob; 1-D tensor of shape (bottom_blob.dims,), `bottom_blob.dims` is the input blob dimensions.</dd>
+</dl>
+
+#### Type Constraints
+
+- ncnn.Mat: Mat(float32)