Add a note about CKEDITOR_BASEPATH

Refs django-ckeditor#347, django-ckeditor#192, django-ckeditor#348, django-ckeditor#346, django-ckeditor#326.

Author: matthiask

docs/INSTALL.md

@@ -32,6 +32,15 @@
 
        CKEDITOR_JQUERY_URL = 'https://ajax.googleapis.com/ajax/libs/jquery/2.2.4/jquery.min.js'
 
+9. CKEditor needs to know where its assets are located because it loads them lazily only when needed. The location is determined by looking at a script tag which includes a URL ending in ``ckeditor.js``. This does not work all the time, for example when using ``ManifestStaticFilesStorage``, any asset packaging pipeline or whatnot. django-ckeditor is quite good at automatically detecting the correct place even then, but sometimes you have to hardcode ``CKEDITOR_BASEPATH`` somewhere. It is recommended to override the ``admin/base_site.html`` template with your own, i.e.::
+
+    {% extends "admin/base_site.html" %}
+
+    {% block extrahead %}
+    <script>window.CKEDITOR_BASEPATH = '/static/ckeditor/ckeditor/';</script>
+    {{ block.super }}
+    {% endblock %}
+
 
 ## Optional