f clarify comment

Author: TheBlueMatt

lightning/src/routing/scoring.rs

@@ -1051,8 +1051,10 @@ fn success_probability(
 			// the amount, divided by the same integral from the minimum to the maximum liquidity
 			// bounds.
 			//
-			// Because the integral is simply a constant times (x - 0.5)^3, this means we simply
-			// subtract the two bounds mius 0.5 to the 3rd power.
+			// Because the integral from x to y is simply (y - 0.5)^3 - (x - 0.5)^3, we can
+			// calculate the cumulative density function between the min/max bounds trivially. Note
+			// that we don't bother to normalize the CDF to total to 1, as it will come out in the
+			// division of num / den.
 			let max_pow = (max - 0.5).powi(3);
 			let num = max_pow - (amount - 0.5).powi(3);
 			let den = max_pow - (min - 0.5).powi(3);