Add note to tutorial about required request in serializer context when using HyperlinkedModelSerializer (#9732)

* Fix : Updated documentation in tutorial 5 leading to error

* Updated docs/tutorial/5-relationships-and-hyperlinked-apis.md

Co-authored-by: Bruno Alla <browniebroke@users.noreply.github.com>

* Missing newline

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Co-authored-by: Bruno Alla <browniebroke@users.noreply.github.com>

docs/tutorial/5-relationships-and-hyperlinked-apis.md

@@ -94,6 +94,22 @@ Notice that we've also added a new `'highlight'` field.  This field is of the sa
 
 Because we've included format suffixed URLs such as `'.json'`, we also need to indicate on the `highlight` field that any format suffixed hyperlinks it returns should use the `'.html'` suffix.
 
+---
+
+**Note:**
+
+When you are manually instantiating these serializers inside your views (e.g., in `SnippetDetail` or `SnippetList`), you **must** pass `context={'request': request}` so the serializer knows how to build absolute URLs. For example, instead of:
+
+    serializer = SnippetSerializer(snippet)
+
+You must write:
+
+    serializer = SnippetSerializer(snippet, context={'request': request})
+
+If your view is a subclass of `GenericAPIView`, you may use the `get_serializer_context()` as a convenience method.
+
+---
+
 ## Making sure our URL patterns are named
 
 If we're going to have a hyperlinked API, we need to make sure we name our URL patterns.  Let's take a look at which URL patterns we need to name.