doc: add code example to process.throwDeprecation property

PR-URL: #29495
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/process.md

@@ -2224,11 +2224,28 @@ added: v0.9.12
 
 * {boolean}
 
-The `process.throwDeprecation` property indicates whether the
-`--throw-deprecation` flag is set on the current Node.js process. See the
+The initial value of `process.throwDeprecation` indicates whether the
+`--throw-deprecation` flag is set on the current Node.js process.
+`process.throwDeprecation` is mutable, so whether or not deprecation
+warnings result in errors may be altered at runtime. See the
 documentation for the [`'warning'` event][process_warning] and the
-[`emitWarning()` method][process_emit_warning] for more information about this
-flag's behavior.
+[`emitWarning()` method][process_emit_warning] for more information.
+
+```console
+$ node --throw-deprecation -p "process.throwDeprecation"
+true
+$ node -p "process.throwDeprecation"
+undefined
+$ node
+> process.emitWarning('test', 'DeprecationWarning');
+undefined
+> (node:26598) DeprecationWarning: test
+> process.throwDeprecation = true;
+true
+> process.emitWarning('test', 'DeprecationWarning');
+Thrown:
+{ [DeprecationWarning: test] name: 'DeprecationWarning' }
+```
 
 ## process.title
 <!-- YAML