* 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>