C++: Add QLDoc comments.

Author: geoffw0

cpp/ql/lib/semmle/code/cpp/security/Overflow.qll

@@ -41,7 +41,8 @@ private predicate stmtDominates(Stmt dominator, Stmt dominated) {
 }
 
 /**
- * Holds if the value of `use` is guarded to be less than something.
+ * Holds if the value of `use` is guarded to be less than something, and `e`
+ * is in code controlled by that guard (where the guard condition held).
  */
 pragma[nomagic]
 predicate guardedLesser(Operation e, Expr use) {
@@ -67,7 +68,8 @@ predicate guardedLesser(Operation e, Expr use) {
 }
 
 /**
- * Holds if the value of `use` is guarded to be greater than something.
+ * Holds if the value of `use` is guarded to be greater than something, and `e`
+ * is in code controlled by that guard (where the guard condition held).
  */
 pragma[nomagic]
 predicate guardedGreater(Operation e, Expr use) {