chore(courses): Recover PR #5693. Create Greek courses list (#6157)

* Create free-courses-gr.md and added JavaScript course

check_urls=free-programming-books.md free-programming-books-gr.md

* Update free-courses-gr.md

* Bumps review EbookFoundation#5693

Recover deleted PR head:
git fetch upstream pull/5693/head:pr/anneiric/5693

anneiric <69729163+anneiric@users.noreply.github.com>

* fix(listings): greek language code `gr` > `el`

language code for greek is `el` not `gr`. See: EbookFoundation/free-programming-books#6070

Applies https://github.com/EbookFoundation/free-programming-books/pull/5693#issuecomment-938647297

* feat(courses): Add greek entry

Link recent created greek courses listing `books/free-courses-el.md` into `README.md`

Resolves EbookFoundation/free-programming-books#5693

* feat(courses): Add greek entry

Link `courses/free-courses-el.md` into `README.md`

Resolves EbookFoundation/free-programming-books#5693
Co-authored-by: Nanneiric <69729163+anneiric@users.noreply.github.com>

README.md

@@ -83,6 +83,7 @@ Please read [CONTRIBUTING](CONTRIBUTING.md). If you're new to GitHub, [welcome](
 + [Finnish](courses/free-courses-fi.md)
 + [French / français](courses/free-courses-fr.md)
 + [German / Deutsch](courses/free-courses-de.md)
++ [Greek / ελληνικά](courses/free-courses-el.md)
 + [Hebrew / עברית](courses/free-courses-he.md)
 + [Hindi / हिंदी](courses/free-courses-hi.md)
 + [Indonesian / Bahasa Indonesia](courses/free-courses-id.md)

courses/free-courses-el.md

+### Index
+
+* [JavaScript](#javascript)
+
+
+### JavaScript
+
+* [Εισαγωγή Στον WEB Προγραμματισμό Με JavaScript](https://kassapoglou.github.io/javascript/javascript-programming.html) - Μιχάλης Κασάπογλου