Update README.md

README.md

@@ -208,7 +208,7 @@ These two blocks enable or disable specific UI elements.
 
 > appends a radio button group element (based on an [HTML input elements of type "radio"](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/radio)) with the given name and label to the UI. If an element with the same name already exists, it is removed before the new one is appended.
 >
-> Radiobutton groups are a bit special as they contain a whole group of radio buttons, each with its own label. As a consequence, after appending a new radio button group element, you will have to define a list of radio buttons using the "append Choice" block - and the value of the whole group (i.e., the associated context item) is the index of the currently checked radio button (or `-1` if no button is checked)
+> Radiobutton groups are a bit special as they contain a whole group of radio buttons, each with its own label. As a consequence, after appending a new radio button group element, you will have to define a list of radio buttons using the "append Choice" block - and the value of the whole group (i.e., the associated context item) is the (0-based) index of the currently checked radio button (or `-1` if no button is checked)
 
 ![appendDropDown](./Screenshots/appendDropDown.png)