docs: add documentation for adding user settings and tooltips (#8634)

Co-authored-by: openhands <openhands@all-hands.dev>

.openhands/microagents/repo.md

@@ -66,3 +66,18 @@ These details may or may not be useful for your current task.
 - Actions with `thought` property are displayed in the UI based on their action type:
   - Regular actions (like "run", "edit") display the thought as a separate message
   - Special actions (like "think") are displayed as collapsible elements only
+
+#### Adding User Settings:
+- To add a new user setting to OpenHands, follow these steps:
+  1. Add the setting to the frontend:
+     - Add the setting to the `Settings` type in `frontend/src/types/settings.ts`
+     - Add the setting to the `ApiSettings` type in the same file
+     - Add the setting with an appropriate default value to `DEFAULT_SETTINGS` in `frontend/src/services/settings.ts`
+     - Update the `useSettings` hook in `frontend/src/hooks/query/use-settings.ts` to map the API response
+     - Update the `useSaveSettings` hook in `frontend/src/hooks/mutation/use-save-settings.ts` to include the setting in API requests
+     - Add UI components (like toggle switches) in the appropriate settings screen (e.g., `frontend/src/routes/app-settings.tsx`)
+     - Add i18n translations for the setting name and any tooltips in `frontend/src/i18n/translation.json`
+     - Add the translation key to `frontend/src/i18n/declaration.ts`
+  2. Add the setting to the backend:
+     - Add the setting to the `Settings` model in `openhands/storage/data_models/settings.py`
+     - Update any relevant backend code to apply the setting (e.g., in session creation)