sysadm: add mirror-operations without content

sysadm/mirror-operations/deploy.rst

+.. _sysadm_mirror_deploy:
+
+How To Deploy a Mirror
+-----------------------

sysadm/mirror-operations/index.rst

+.. _sysadm_mirror_operations:
+
+Mirror Operations
+-----------------
+
+A mirror is a full copy of the |swh| archive, operated independently from the
+Software Heritage initiative.
+
+A mirror should be able to:
+- store a full copy of the archive,
+- serve the data using the web UI,
+- search the archive using the web UI,
+- serve the data using the public API,
+- allow users to retrieve the content from the archive using the Vault service
+  (swh-vault).
+
+
+See the :ref:`swh-devel:mirror` for a complete description of the mirror
+architecture.
+
+.. toctree::
+   :titlesonly:
+
+   deploy
+   onboard
+   monitor

sysadm/mirror-operations/monitor.rst

+.. _sysadm_mirror_monitor:
+
+Monitor a Mirror
+----------------

sysadm/mirror-operations/onboard.rst

+.. _sysadm_mirror_onboard:
+
+How To Onboard a Mirror
+-----------------------