slack_importer_doc: Fix outdated links.

Existing links redirects to irrelevant documentation pages.

(cherry picked from commit b36f09c67f)

help/import-from-slack.md

@@ -67,14 +67,14 @@ in order to export direct message data.
    scratch" creation option.
 
 1. [Create a
-   bot user](https://api.slack.com/authentication/basics#scopes),
+   bot user](https://docs.slack.dev/app-management/quickstart-app-settings/#creating),
    following the instructions to add the following OAuth scopes to your bot:
     - `emoji:read`
     - `users:read`
     - `users:read.email`
     - `team:read`
 
-1. [Install your new app](https://api.slack.com/authentication/basics#installing)
+1. [Install your new app](https://docs.slack.dev/app-management/quickstart-app-settings/#installing)
    to your Slack workspace.
 
 1. You will immediately see a **Bot User OAuth Token**, which is a long