emacs: add config for markdown-mode

emacs/init.el

@@ -113,7 +113,12 @@
   :hook (haskell-mode . agw-fp-mode))
 
 (use-package markdown-mode
-  :ensure t)
+  :ensure t
+  :hook ((markdown-mode . variable-pitch-mode)
+         (markdown-mode . flyspell-mode))
+  :config
+  (dolist (face '(markdown-inline-code markdown-code))
+    (set-face-attribute face nil :inherit 'fixed-pitch)))
 
 (use-package ruby-mode
   :init