Note dependancies in docs

docs/topics/3.6-announcement.md

@@ -60,6 +60,10 @@ REST framework's new API documentation supports a number of features:
 * Support for various authentication schemes.
 * Code snippets for the Python, JavaScript, and Command Line clients.
 
+The `coreapi` library is required as a dependancy for the API docs. Make sure
+to install the latest version (2.3.0 or above). The `pygments` and `markdown`
+libraries are optional but recommended.
+
 To install the API documentation, you'll need to include it in your projects URLconf:
 
     from rest_framework.documentation import include_docs_urls
@@ -147,6 +151,11 @@ For more information see the [Python client library documentation][py-docs].
 
 ## Deprecations
 
+### Updating `coreapi`
+
+If you're using REST framework's schema generation, or want to use the API docs,
+then you'll need to update to the latest version of coreapi. (2.3.0)
+
 ### Generating schemas from Router
 
 The 3.5 "pending deprecation" of router arguments for generating a schema view, such as `schema_title`, `schema_url` and `schema_renderers`, have now been escalated to a

docs/topics/documenting-your-api.md

@@ -16,6 +16,10 @@ The built-in API documentation includes:
 
 ### Installation
 
+The `coreapi` library is required as a dependancy for the API docs. Make sure
+to install the latest version. The `pygments` and `markdown` libraries
+are optional but recommended.
+
 To install the API documentation, you'll need to include it in your projects URLconf:
 
     from rest_framework.documentation import include_docs_urls