add blurb on how to add image upload support

Author: enriquegh

docs/cody/capabilities/chat.mdx

@@ -84,6 +84,18 @@ Once uploaded, you can ask Cody questions about the image, such as:
 
 Image upload support varies by client. Check the [feature parity reference](/cody/clients/feature-reference#chat) to see which clients support image upload.
 
+### Enterprise configuration
+
+For Sourcegraph Enterprise users, site admins must enable the `chatVision` feature in the site configuration for image uploads to work:
+
+```json
+"configFeatures": {
+  "chatVision": true
+}
+```
+
+See the [site configuration reference](/admin/config/site_config) for more details.
+
 ## LLM selection
 
 Cody allows you to select the LLM you want to use for your chat, which is optimized for speed versus accuracy. Enterprise users with the new [model configuration](/cody/clients/model-configuration) can use the LLM selection dropdown to choose a chat model.