refactor(org): org-src-lang-modes: move md alias

This is a general convenience for org users, not specifically for users
of the markdown module, so it belongs in :lang org.

modules/lang/org/config.el

@@ -205,6 +205,9 @@ Is relative to `org-directory', unless it is absolute. Is used in Doom's default
         ;; Our :lang common-lisp module uses sly, so...
         org-babel-lisp-eval-fn #'sly-eval)
 
+  ;; A shorter alias for markdown code blocks.
+  (add-to-list 'org-src-lang-modes '("md" . markdown))
+
   ;; I prefer C-c C-c over C-c ' (more consistent)
   (define-key org-src-mode-map (kbd "C-c C-c") #'org-edit-src-exit)