Add some documentation for Helix mode (#35641)

Because there is literally no mention of it in the docs

Release Notes:

- N/A

---------

Co-authored-by: ponychicken <183302+ponychicken@users.noreply.github.com>
Co-authored-by: Ben Kunkle <ben@zed.dev>

docs/src/configuring-zed.md

@@ -3195,10 +3195,16 @@ Run the `theme selector: toggle` action in the command palette to see a current
 
 ## Vim
 
-- Description: Whether or not to enable vim mode (work in progress).
+- Description: Whether or not to enable vim mode. See the [Vim documentation](./vim.md) for more details on configuration.
 - Setting: `vim_mode`
 - Default: `false`
 
+## Helix Mode
+
+- Description: Whether or not to enable Helix mode. Enabling `helix_mode` also enables `vim_mode`. See the [Helix documentation](./helix.md) for more details.
+- Setting: `helix_mode`
+- Default: `false`
+
 ## Project Panel
 
 - Description: Customize project panel