Add link to the documentation page

Problem/Motivation

There is no link to the module documentation page at https://www.drupal.org/docs/drupal-apis/migrate-api/migrate-destination-... → .

Steps to reproduce

Scan "Resources" on the project page https://www.drupal.org/project/migrate_file → , and find no documentation.

Proposed resolution

Add a "Documentation" link under "Resources" on project page, pointing at https://www.drupal.org/docs/drupal-apis/migrate-api/migrate-destination-... → .

Remaining tasks

User interface changes

API changes

Data model changes