Add Emacs Lisp Elements book

[DavideDunne]

What does this PR do?

Add resource(s)

For resources

Description

Add Emacs Lisp Elements book
This is a book for explaining Emacs Lisp, unlike An Introduction to Programming in Emacs Lisp is not an introduction to programming with elisp, but only an introduction to using Emacs Lisp

Why is this valuable (or not)?

There are very few Emacs Lisp resources for reading, the only book that I know dedicated only to Elisp is An Introduction to Programming in Emacs Lisp

How do we know it's really free?

All available online, no paywalls, can read it directly from HTML or through the GitHub repo.
Legally speaking, it's licensed under the GNU Free Documentation License

For book lists, is it a book? For course lists, is it a course? etc.

The author considers it a book

Checklist:

• Read our contributing guidelines.
• Search for duplicates.
• Include author(s) and platform where appropriate.
• Put lists in alphabetical order, correct spacing.
• Add needed indications (PDF, access notes, under construction).
• Used an informative name for this pull request.

Follow-up

• Check the status of GitHub Actions and resolve any reported warnings!

[github-actions]

Linter failed, fix the error(s):

free-programming-books/books/free-programming-books-langs.md
1556:1-1559:104  warning  Alphabetical ordering: swap l.1559 and l.1558  alphabetize-lists  remark-lint

[eshellman]

Thanks, and welcome to free-programming-books!