docs: Clarify how to turn edit predictions off (#27592)

Closes https://github.com/zed-industries/zed/issues/27590

Release Notes:

- N/A

docs/src/completions.md

@@ -32,15 +32,9 @@ Clicking on it would take you to a modal with a button ("Enable Edit Prediction"
 
 ![Onboarding banner and modal](https://zed.dev/img/edit-prediction/docs.webp)
 
-But, if you haven't come across the banner, start using Zed's Edit Prediction by adding this to your settings:
+But, if you haven't come across the banner, Zed's Edit Prediction is the default edit prediction provider and you should see it right away in your status bar.
 
-```json
+### Switching modes {#switching-modes}
-"features": {
-  "edit_prediction_provider": "zed"
-},
-```
-
-### Switching modes
 
 Zed's Edit Prediction comes with two different display modes:
 
@@ -224,7 +218,7 @@ If you would like to use the default keybinding, you can free it up by either mo
 
 ## Disabling Automatic Edit Prediction
 
-To disable predictions that appear automatically as you type, set this within `settings.json`:
+To not have predictions appear automatically as you type, set this within `settings.json`:
 
 ```json
 {
@@ -246,6 +240,18 @@ You can also add this as a language-specific setting in your `settings.json` to
 }
 ```
 
+Alternatively, if you're using Zed's Edit Prediction, you can [use Subtle Mode](/#switching-modes).
+
+### Turning Off Completely
+
+To completely turn off edit prediction across all providers, explicitly set the settings to `none`, like so:
+
+```json
+"features": {
+  "edit_prediction_provider": "none"
+},
+```
+
 ## Configuring GitHub Copilot {#github-copilot}
 
 To use GitHub Copilot, set this within `settings.json`: