docs: added admin trick to unarchive an repository

docs/admin/admin-tricks.rst

@@ -239,3 +239,26 b' following URL: ``{instance-URL}/_admin/p'
 
 .. _Markdown: http://daringfireball.net/projects/markdown/
 .. _reStructured Text: http://docutils.sourceforge.net/docs/index.html
+
+
+Unarchiving a repository
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Archive operation for the repository is similar as delete. Archive keeps the data for future references
+but makes the repository read-only. After archiving the repository it shouldn't be modified in any way.
+This is why repository settings are disabled for an archived repository.
+
+If there's a need for unarchiving a repository for some reasons, the interactive
+ishell interface should be used.
+
+.. code-block:: bash
+
+  # Open iShell from the terminal
+  $ rccontrol ishell enterprise-1/community-1
+
+.. code-block:: python
+
+  # Set repository as un-archived
+  In [1]: repo = Repository.get_by_repo_name('SOME_REPO_NAME')
+  In [2]: repo.archived = False
+  In [3]: Session().add(repo);Session().commit()