Update documentation

Author: paulorb

docs/getting-started/operations.md

@@ -11,4 +11,22 @@ Set (as the name implies) set a certain value to a variable, like the example be
 ```
 
 Both **symbol** and **value** are mandatory fields. **value** can be of type *FLOAT32* , *INT16* or *BOOL* which must
-follow the same type of the specified **symbol** definition. In case the variable already is initialized, it overwrites the value.
+follow the same type of the specified **symbol** definition. In case the variable already is initialized, it overwrites the value.
+
+Supported registers: **HOLDING_REGISTER**, **COIL**, **DISCRETE_INPUT**, **INPUT_REGISTER**
+
+## Add
+Add (as the name implies) add a certain value to a variable, like the example below:
+
+```xml
+ <add symbol="MOTOR_SPEED1">15.5</add>
+```
+
+Both **symbol** and **value** are mandatory fields. **value** can be of type *FLOAT32* , *INT16*  which must
+follow the same type of the specified **symbol** definition.
+
+Supported registers: **HOLDING_REGISTER**, **INPUT_REGISTER** 
+
+*For **INPUT_REGISTER**  type *FLOAT32* is not supported!*
+
+