chore(doc): replace '"follow.start"' with '"hint.quick"' (#515)

Replace `follow.start` with `hint.quick`. The `hint.quick` actions is
the current default and `follow.start` is an alias to keep a
compatibility.

close #512

docs/keymaps.md

@@ -73,13 +73,13 @@ See the [console commands](./console_commands) section for a more detailed descr
 
 Vimmatic can be configured to follow links opened in tabs in the background
 instead of switching to a new tab immediately. To do this, you'll need to update
-the config file: change the `"background"` property of the `"follow.start"`
+the config file: change the `"background"` property of the `"hint.quick"`
 action to `true`, e.g.:
 
 ```json
 {
     "keymaps": {
-        "F": { "type": "follow.start", "newTab": true, "background": true }
+        "F": { "type": "hint.quick", "newTab": true, "background": false }
     }
 }
 ```