Who sees which manual 

Access follows the dashboard: a user sees a manual if the widget is allowed for one of their backend groups. Admins see all manuals.

  1. Edit the backend user group: module Administration > Users, or the group record in the page tree root.
  2. Tab Module Permissions: allow the module Dashboard, and tick the manual under Allowed dashboard widgets.

The user then adds the widget via Dashboard > + > Documentation.

Give new users the widget straight away 

Add a dashboard preset to your sitepackage:

Configuration/Backend/DashboardPresets.php 
<?php

return [
    'mySitepackageEditors' => [
        'title' => 'my_sitepackage.messages:dashboard.editors',
        'description' => 'my_sitepackage.messages:dashboard.editors.description',
        'iconIdentifier' => 'content-dashboard',
        'defaultWidgets' => ['mySitepackageManual'],
        'showInWizard' => true,
    ],
];
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and select it for the group in its user TSconfig:

User TSconfig of the backend group 
options.dashboard.dashboardPresetsForNewUsers = mySitepackageEditors
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