Add review comments for migration of servlets for RESTEasy Reactive

docs/src/main/asciidoc/resteasy-reactive-migration.adoc

@@ -124,10 +124,30 @@ when the method returns a `String`.
 
 RESTEasy Reactive does **not** support servlets.
 If your project depends on servlets you have to migrate them.
-A common situation is when your application is developed with JAX-RS for a servlet-based environment.
 A servlet-based JAX-RS implementation must support injections of these types with the `@Context` annotation: `ServletConfig`, `ServletContext`, `HttpServletRequest` and `HttpServletResponse`.
-Since RESTEasy Reactive is not servlet-based these injections are not mandatory.
+Since RESTEasy Reactive is not servlet-based these injections will not work.
+
 It is not always obvious that this will fail especially if you depend on an extension like `quarkus-undertow` which supplies the interfaces.
+For example, if you write this you could compile it but get an exception on calling it:
+
+[source, java]
+----
+@Path("/reactive")
+public class ReactiveResource {
+
+    @Context
+    HttpServletRequest httpServletRequest;
+
+    @GET
+    @Produces(MediaType.TEXT_PLAIN)
+    public String servletContextPath() {
+
+        String contextPath = httpServletRequest.getContextPath();
+
+        return "My context path is: " + contextPath;
+    }
+}
+----
 
 The same is true for your third-party libraries.
 If they happen to depend on servlets you need to find a migration path for them.