[DOCS] Add missing modules

docs/modules/index.md

@@ -12,8 +12,9 @@ following links.
 
 ## What's a module?
 
-Prelude modules are plain old Elisp libraries - there's absolutely nothing magical about them.
-Most of them simply install a few Emacs packages and provide some sensible baseline configuration for them.
+Prelude modules are plain old Elisp libraries - there's absolutely
+nothing magical about them.  Most of them simply install a few Emacs
+packages and provide some sensible baseline configuration for them.
 Here's a real example.
 
 ``` emacs-lisp
@@ -28,10 +29,14 @@ Here's a real example.
 ;; We never want to edit Rubinius bytecode
 (add-to-list 'completion-ignored-extensions ".rbc")
 
+;; Map yari to C-h R
 (define-key 'help-command (kbd "R") 'yari)
 
 (with-eval-after-load 'ruby-mode
   (defun prelude-ruby-mode-defaults ()
+    ;; Don't auto-insert encoding comments
+    ;; Those are almost never needed in Ruby 2+
+    (setq ruby-insert-encoding-magic-comment nil)
     (inf-ruby-minor-mode +1)
     ;; CamelCase aware editing operations
     (subword-mode +1))
@@ -57,20 +62,22 @@ The following programming languages have enhanced support in Prelude:
 - [Common Lisp](common_lisp.md)
 - CSS
 - [Dart](dart.md)
+- Elixir
 - [Emacs Lisp](emacs_lisp.md)
 - Erlang
-- Elixir
 - Go
 - Haskell
 - JavaScript
 - LaTeX
 - [Lisp Base](lisp.md) (common foundation for Lisp modules)
 - LSP (common foundation for all modules relying on `lsp-mode`)
+- Lua
 - Markdown
 - OCaml
 - Perl
-- [Python](python.md)
 - [Programming Base](programming.md) (common foundation for programming modules)
+- [Python](python.md)
+- Racket
 - [Ruby](ruby.md)
 - Rust
 - Scala
@@ -92,3 +99,4 @@ The following programming languages have enhanced support in Prelude:
 - ivy
 - key-chord
 - Org Mode
+- selectrum