Clarify wieght traits needed to impl in example (#9842)

* Clarify wieght traits needed to impl in example

* Update frame/example/src/lib.rs

* Update frame/example/src/lib.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* fmt

Co-authored-by: Squirrel <gilescope@gmail.com>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

substrate/frame/example/src/lib.rs

@@ -486,11 +486,12 @@ pub mod pallet {
 		// the chain in a moderate rate.
 		//
 		// The parenthesized value of the `#[pallet::weight(..)]` attribute can be any type that
-		// implements a set of traits, namely [`WeighData`] and [`ClassifyDispatch`].
-		// The former conveys the weight (a numeric representation of pure execution time and
-		// difficulty) of the transaction and the latter demonstrates the [`DispatchClass`] of the
-		// call. A higher weight means a larger transaction (less of which can be placed in a
-		// single block).
+		// implements a set of traits, namely [`WeighData`], [`ClassifyDispatch`], and
+		// [`PaysFee`]. The first conveys the weight (a numeric representation of pure
+		// execution time and difficulty) of the transaction and the second demonstrates the
+		// [`DispatchClass`] of the call, the third gives whereas extrinsic must pay fees or not.
+		// A higher weight means a larger transaction (less of which can be placed in a single
+		// block).
 		//
 		// The weight for this extrinsic we rely on the auto-generated `WeightInfo` from the
 		// benchmark toolchain.