docs(guides): add warning about varying output as discussed in #1356

Author: skipjack

content/guides/index.md

@@ -1,7 +1,12 @@
 ---
 title: Guides
+sort: 0
+contributors:
+  - skipjack
 ---
 
 This section contains guides for understanding and mastering the wide variety of tools and features that webpack offers. The first is a simple guide that takes you through [installation](/guides/installation).
 
 The guides get more and more advanced as you go on. Most serve as a starting point, and once completed you should feel more comfortable diving into the actual [documentation](/configuration).
+
+W> The output shown from running webpack in the guides may differ slightly from the output of newer versions. This is to be expected. As long as the bundles look similar and run correctly, then there shouldn't be any issues. If you do come across an example that seems to be broken by a new version, please create an issue and we will do our best to resolve the discrepancy.