Bind "j k" to NormalBefore in initial keymap examples (#34912)

It looks like typically vim configurations bind "j k" to be the same as
escape, which has the "NormalBefore" behavior positioning the block
cursor on the character before the insertion cursor. The [vim mode
docs](https://zed.dev/docs/vim#useful-contexts-for-vim-mode-key-bindings)
also use NormalBefore here.

Thanks to @omniwrench for mentioning this in
https://github.com/zed-industries/zed/discussions/6661#discussioncomment-13848043
. This was a mistake in #31163.

Release Notes:

- N/A

assets/keymaps/initial.json

@@ -15,7 +15,7 @@
   {
     "context": "Editor && vim_mode == insert && !menu",
     "bindings": {
-      // "j k": "vim::SwitchToNormalMode"
+      // "j k": "vim::NormalBefore"
     }
   }
 ]