docs: Document how STATIC_URL_BASE is used (#36952)

cms/envs/common.py

@@ -1196,6 +1196,10 @@ COURSE_METADATA_EXPORT_BUCKET = ''
 
 ALTERNATE_WORKER_QUEUES = 'lms'
 
+# .. setting_name: STATIC_URL_BASE
+# .. setting_default: "/static/"
+# .. setting_description: The CMS uses this to construct ``STATIC_URL`` by appending
+#   a slash (if needed) and then ``studio/``.
 STATIC_URL_BASE = '/static/'
 
 X_FRAME_OPTIONS = 'DENY'

lms/envs/common.py

@@ -1920,6 +1920,10 @@ MANAGERS = ADMINS
 # Static content
 STATIC_URL = '/static/'
 STATIC_ROOT = os.environ.get('STATIC_ROOT_LMS', ENV_ROOT / "staticfiles")
+# .. setting_name: STATIC_URL_BASE
+# .. setting_default: "/static/"
+# .. setting_description: The LMS uses this to construct ``STATIC_URL`` by appending
+#   a slash (if needed).
 STATIC_URL_BASE = '/static/'
 
 STATICFILES_DIRS = [