Rephrase slightly tricky idea

I started by just fixing a typo ("radio groups ... are a group") but
quickly saw this is a little tough to parse even after fixing the typo.

I rephrased the sentence to make it a little more explicit and verbose,
and I think it's a little easier to understand.

Author: ianjmacintosh

exercises/08.inputs/03.problem.radio/README.mdx

@@ -8,10 +8,10 @@ that's the best option. Instead, let's use a radio group.
 
 📜 You can [learn about radio groups on MDN](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/radio)
 
-What's interesting about radio groups is that they are a group of inputs that
-share the same name. Only one of them can be selected at a time. Each radio
-input needs its own `label`. To label the entire group, you can use a
-`<fieldset>` and a `<legend>`.
+What's interesting about radio groups is that each radio group can contain
+multiple inputs that share the same name. Only one of them can be selected at
+a time. Each radio input needs its own `label`. To label the entire group, you
+can use a `<fieldset>` and a `<legend>`.
 
 Similar to checkboxes, to set the default value, you need to add the `checked`
 attribute to the input you want to be selected by default.