Add example of author>authors front-matter replacement

Ref: https://github.com/MunifTanjim/minimo/issues/142

test/site/content-org/all-posts.org

@@ -5121,6 +5121,14 @@ This post will have the =foo= key in front-matter replaced with
 :END:
 Here, attempt is made to replace a non-existing key =toto=, but still,
 there shouldn't be any error.
+*** Make the author front-matter plural                              :author:
+:PROPERTIES:
+:EXPORT_FILE_NAME: plural-author-front-matter
+:EXPORT_AUTHOR: Mark Twain, Arthur Conan Doyle
+:EXPORT_HUGO_FRONT_MATTER_KEY_REPLACE: author>authors
+:END:
+Some themes might expect the front-matter list variable for authors to
+be ~authors~ instead of the default ~author~ created by ~ox-hugo~.
 * Date and slug inheritance                           :inheritance:date:slug:
 :PROPERTIES:
 :EXPORT_DATE: 2018-02-12

test/site/content/posts/plural-author-front-matter.md

@@ -0,0 +1,9 @@
++++
+title = "Make the author front-matter plural"
+authors = ["Mark Twain", "Arthur Conan Doyle"]
+tags = ["front-matter", "keys", "replace", "author"]
+draft = false
++++
+
+Some themes might expect the front-matter list variable for authors to
+be `authors` instead of the default `author` created by `ox-hugo`.