Note django-filter installation

docs/index.md

@@ -32,7 +32,7 @@ REST framework requires the following:
 
 The following packages are optional:
 
-* [Markdown][markdown] (2.1.0+) - Markdown support for the self describing API.
+* [Markdown][markdown] (2.1.0+) - Markdown support for the browseable API.
 * [PyYAML][yaml] (3.10+) - YAML content-type support.
 * [django-filter][django-filter] (master) - Filtering support.
 
@@ -41,8 +41,9 @@ The following packages are optional:
 Install using `pip`, including any optional packages you want...
 
     pip install djangorestframework
-    pip install markdown  # Recommended if using the browseable API.
-    pip install pyyaml    # Required for yaml content-type support.
+    pip install markdown  # Markdown support for the browseable API.
+    pip install pyyaml    # YAML content-type support.
+    pip install -e git+https://github.com/alex/django-filter.git#egg=django-filter  # Filtering support
 
 ...or clone the project from github.