Different approach to the clarification

Rather than a recap at the end, the introduction reminds the reader of what has gone before.

Author: mpilgrem

doc/GUIDE.md

@@ -447,22 +447,20 @@ Remember above when `stack new` selected some
 our build plan and available packages. When we tried using the `text` package,
 it just worked, because it was part of the LTS *package set*.
 
-But `acme-missiles` is not part of that package set, so building failed.
+We've specified the `acme-missiles` package in the `package.yaml` file (see
+above), but `acme-missiles` is not part of that LTS package set, so building
+failed.
 
-To add this new dependency, we'll use the `extra-deps` field in `stack.yaml` to
-define extra dependencies not present in the resolver. You can add this like so:
+To add `acme-missles` to the available packages, we'll use the `extra-deps`
+field in the `stack.yaml` file. That field defines extra packages, not present
+in the resolver, that will be needed as dependencies. You can add this like so:
 
 ```yaml
 extra-deps:
-- acme-missiles-0.3 # not in the LTS
+- acme-missiles-0.3 # not in the LTS resolver
 ```
 
-Now `stack build` will succeed.  To recap you needed to 
-* add `acme-missiles` to **dependencies** in `package.yaml` and
-* add `acme-missiles-0.3` to **extra-deps** in `stack.yaml`
-
-If you failed to do this you may experience 
-[Could not find module ‘Acme.Missiles’](https://stackoverflow.com/questions/48251027/cannot-add-extra-deps-to-stack-project)
+Now `stack build` will succeed.
 
 With that out of the way, let's dig a little bit more into these package sets,
 also known as *snapshots*. We mentioned the LTS resolvers, and you can get quite