Update configuration documentation

docs/docs/getting-started/configuration.md

@@ -23,6 +23,24 @@ Ransack.configure do |config|
   # This can also be configured individually in each sort link (see the README).
   config.hide_sort_order_indicators = true
 
+  # By default, Ransack displays sort order indicator arrows with HTML codes, but
+  # these can be overridden.
+  config.custom_arrows = {
+    up_arrow:   '<i class="fa fa-long-arrow-up"></i>', # default: '&#9660;'
+    down_arrow: 'U+02193',                             # default: '&#9650;'
+    default_arrow: 'U+11047'                           # default: nil 
+  }
+
+  # Ransack sanitizes many values in your custom scopes into booleans.
+  # You can turn this off for custom scopes.
+  config.sanitize_custom_scope_booleans = false
+
+  # Configure a default predicate if an unknown predicate is passed; setting it to
+  # e.g. 'eq' allows for allowing for exact matches by just the attribute name.
+  config.default_predicate = 'eq'
+
+  # Postgres has a nulls first / nulls last option, this can be configured.
+  config.postgres_fields_sort_option = :nulls_first # or e.g. :nulls_always_last
 end
 ```