ntp: add next-steps docs (#1290)

Co-authored-by: Shane Osbourne <[email protected]>

Author: shakyShane

special-pages/pages/new-tab/app/new-tab.md

@@ -6,6 +6,7 @@ children:
   - ./update-notification/update-notification.md
   - ./privacy-stats/privacy-stats.md
   - ./favorites/favorites.md
+  - ./next-steps/next-steps.md
 ---
 
 ## Requests

…tab/app/next-steps/next-steps.service.md …ges/new-tab/app/next-steps/next-steps.mdspecial-pages/pages/new-tab/app/next-steps/next-steps.service.md renamed to special-pages/pages/new-tab/app/next-steps/next-steps.md special-pages/pages/new-tab/app/next-steps/next-steps.service.md renamed to special-pages/pages/new-tab/app/next-steps/next-steps.md

@@ -2,10 +2,37 @@
 title: Next Steps Cards
 ---
 
+## Setup
+
+- Widget ID: `nextSteps`
+- Add it to the `widgets` field on [initialSetup](../new-tab.md)
+- Example:
+
+```json
+{
+  "...": "...",
+  "widgets": [
+    {"id":  "nextSteps"},
+    {"...":  "..."}
+  ]
+}
+```
+
 ## Requests:
 - {@link "NewTab Messages".NextStepsGetDataRequest `nextSteps_getData`}
     - Used to fetch the initial data (during the first render)
-    - returns {@link "NewTab Messages".NextStepsData}
+    - returns {@link "NewTab Messages".NextStepsData} - either `null` or `Array<{id: string}>`
+    - Note: Please use `null` to represent when there's nothing to show (instead of an empty array.)
+    - IDs: Please find the list of supported IDs here {@link "NewTab Messages".NextStepsCards}
+    - Example:
+
+```json
+[
+  { "id": "bringStuff" },
+  { "id": "defaultApp" }
+]
+```
+
 - {@link "NewTab Messages".NextStepsGetConfigRequest `nextSteps_getConfig`}
     - Used to fetch the initial config (during the first render)
     - returns {@link "NewTab Messages".NextStepsConfig}
@@ -14,8 +41,9 @@ title: Next Steps Cards
 - {@link "NewTab Messages".NextStepsOnDataUpdateSubscription `nextSteps_onDataUpdate`}.
     - The messages available for the platform
     - returns {@link "NewTab Messages".NextStepsData}
+    - as mentioned in the request, please use `null` to represent when there's nothing to show (instead of an empty array.)
 - {@link "NewTab Messages".NextStepsOnConfigUpdateSubscription `nextSteps_onConfigUpdate`}.
-    - The widget config
+    - The widget-specific config, to toggle things like the expansion
     - returns {@link "NewTab Messages".NextStepsConfig}
 
 ## Notifications: