Shared: Add an example for SemBound.getExpr.

Author: geoffw0

shared/rangeanalysis/codeql/rangeanalysis/RangeAnalysis.qll

@@ -393,7 +393,9 @@ signature module BoundSig<LocationSig Location, Semantic Sem, DeltaSig D> {
     Location getLocation();
 
     /**
-     * Gets an expression that equals this bound plus `delta`.
+     * Gets an expression that equals this bound plus `delta`. For example given
+     * the expression `x = foo() + 1` the variable `x` has a bound with
+     * expression `call to foo()` and delta `-1`.
      *
      * For the zero-bound this gets integer constants equal to `delta`, and for
      * other bounds this gets expressions equal to the bound while `delta = 0`.