[engines] move library of genesis from general to files category

searx/settings.yml

@@ -806,7 +806,7 @@ engines:
     url_xpath: //a[contains(@href,"bookfi.net/md5")]/@href
     title_xpath: //a[contains(@href,"book/")]/text()[1]
     content_xpath: //td/a[1][contains(@href,"=author")]/text()
-    categories: general
+    categories: files
     timeout: 7.0
     disabled: true
     shortcut: lg