Swish specification refactoring (#5015)

* Review spec of Swish operation

* Change reference link to abstract

* Minor change in example section

* Fix minor wording issues

docs/ops/activation/Swish_4.md

@@ -2,38 +2,40 @@
 
 **Versioned name**: *Swish-4*
 
-**Category**: *Activation*
+**Category**: *Activation function*
 
-**Short description**: Swish takes one input tensor and produces output tensor where the Swish function is applied to the tensor elementwise.
+**Short description**: *Swish* performs element-wise activation function on a given input tensor.
 
-**Detailed description**: For each element from the input tensor calculates corresponding
-element in the output tensor with the following formula: 
+**Detailed description**
+
+*Swish* operation is introduced in this [article](https://arxiv.org/abs/1710.05941).
+It performs element-wise activation function on a given input tensor, based on the following mathematical formula:
 
 \f[
-Swish(x) = x / (1.0 + e^{-(beta * x)})
+Swish(x) = x\cdot \sigma(\beta x) = x \left(1 + e^{-(\beta x)}\right)^{-1}
 \f]
 
-The Swish operation is introduced in the [article](https://arxiv.org/pdf/1710.05941.pdf).
+where β corresponds to `beta` scalar input.
 
-**Attributes**:
+**Attributes**: *Swish* operation has no attributes.
 
 **Inputs**:
 
-*   **1**: Multidimensional input tensor of type *T*. **Required**.
+*   **1**: `data`. A tensor of type `T` and arbitrary shape. **Required**.
 
-*   **2**: Scalar with non-negative value of type *T*. Multiplication parameter *beta* for the sigmoid. If the input is not connected then the default value 1.0 is used. **Optional**
+*   **2**: `beta`. A non-negative scalar value of type `T`. Multiplication parameter for the sigmoid. Default value 1.0 is used. **Optional**.
 
 **Outputs**:
 
-*   **1**: The resulting tensor of the same shape and type as input tensor.
+*   **1**: The result of element-wise *Swish* function applied to the input tensor `data`. A tensor of type `T` and the same shape as `data` input tensor.
 
 **Types**
 
-* *T*: arbitrary supported floating point type.
+* *T*: arbitrary supported floating-point type.
 
+**Examples**
 
-**Example**
-
+*Example: Second input `beta` provided*
 ```xml
 <layer ... type="Swish">
     <input>
@@ -41,13 +43,30 @@ The Swish operation is introduced in the [article](https://arxiv.org/pdf/1710.05
             <dim>256</dim>
             <dim>56</dim>
         </port>
-        <port id="1"/>
+        <port id="1">  <!-- beta value: 2.0 -->
+        </port>
     </input>
     <output>
-        <port id="1">
+        <port id="2">
             <dim>256</dim>
             <dim>56</dim>
         </port>
     </output>
 </layer>
-```
+```
+
+*Example: Second input `beta` not provided*
+```xml
+<layer ... type="Swish">
+    <input>
+        <port id="0">
+            <dim>128</dim>
+        </port>
+    </input>
+    <output>
+        <port id="1">
+            <dim>128</dim>
+        </port>
+    </output>
+</layer>
+```