Update python/ql/src/semmle/python/functions/ModificationOfParameterWithDefaultCustomizations.qll

Co-authored-by: Rasmus Wriedt Larsen <rasmuswriedtlarsen@gmail.com>

Author: yoff

python/ql/src/semmle/python/functions/ModificationOfParameterWithDefaultCustomizations.qll

@@ -141,9 +141,17 @@ module ModificationOfParameterWithDefault {
   private import semmle.python.essa.SsaCompute
 
   /**
-   * Simple detection of truthy and falsey values.
+   * A data-flow node that is known to be either truthy or falsey.
    *
    * It handles the cases `if x` and `if not x`.
+   * 
+   * For example, in the following code, `this` will be the `x` that is printed,
+   * which we will know is truthy:
+   * 
+   * ```py
+   * if x:
+   *     print(x)
+   * ```
    */
   private class MustBe extends DataFlow::Node {
     DataFlow::GuardNode guard;