Polish multilang mode, update docs

assets/_custom.scss

@@ -1 +1,3 @@
-/* To be overridden by theme user, scss variables are also accessible here */
+/* You can add custom styles here. */
+
+// @import "plugins/numbered";

assets/_variables.scss

@@ -1 +1,3 @@
-/* To be overridden by theme user, e.g. set SASS vars*/
+/* You can override SASS variables here. */
+
+// @import "plugins/dark";

assets/search-data.js

@@ -1,7 +1,7 @@
 'use strict';
 
 (function() {
-  const indexCfg = {{ with .Site.Params.BookSearchConfig }}
+  const indexCfg = {{ with .Scratch.Get "bookSearchConfig" }}
     {{ . }};
   {{ else }}
    {};

assets/search.js

@@ -1,6 +1,6 @@
 'use strict';
 
-{{ $searchDataFile := printf "%s.%s" .Language.Lang "search-data.js" }}
+{{ $searchDataFile := printf "%s.search-data.js" .Language.Lang }}
 {{ $searchData := resources.Get "search-data.js" | resources.ExecuteAsTemplate $searchDataFile . | resources.Minify | resources.Fingerprint }}
 
 (function() {