Add Greek translation of the tutorial

* etc/tutorials/TUTORIAL.el_GR: Add tutorial in Greek.  It is a
faithful translation of the TUTORIAL.
* etc/tutorials/TUTORIAL.translators (Author): Mention myself as
the author and the maintainer.
* etc/NEWS: Announce it.  (Bug#55314)

* lisp/language/greek.el (set-language-info-alist): Link to the
tutorial and include sample text.

lisp/language/greek.el

@@ -79,7 +79,9 @@
 	   (coding-priority greek-iso-8bit)
 	   (nonascii-translation . iso-8859-7)
 	   (input-method . "greek")
-	   (documentation . t)))
+	   (documentation . "Support for Greek ISO-8859-7 using the greek input method.")
+           (sample-text . "Greek (ελληνικά)	Γειά σας")
+           (tutorial . "TUTORIAL.el_GR")))
 
 (provide 'greek)