bindings: add common comment toggle

This is fairly common in most editors so let's make lives easier.

core/autoload/editor.el

@@ -270,6 +270,16 @@ Respects `require-final-newline'."
   (when (looking-at "\n+")
     (replace-match "")))
 
+;;;###autoload
+(defun doom/toggle-comment-region-or-line ()
+  "Comments or uncomments the whole region or if no region is
+selected, then the current line."
+  (interactive)
+  (let (beg end)
+    (if (region-active-p)
+        (setq beg (region-beginning) end (region-end))
+      (setq beg (line-beginning-position) end (line-end-position)))
+    (comment-or-uncomment-region beg end)))
 
 ;;
 ;; Advice

modules/config/default/config.el

@@ -156,6 +156,7 @@
         "s--" #'text-scale-decrease
         ;; Conventional text-editing keys & motions
         "s-a" #'mark-whole-buffer
+        "s-/" #'doom/toggle-comment-region-or-line
         :gi [s-return]    #'+default/newline-below
         :gi [s-S-return]  #'+default/newline-above
         :gi [s-backspace] #'doom/backward-kill-to-bol-and-indent