Add tutorial to subscribe to package updates

Signed-off-by: Keshav Priyadarshi <git@keshav.space>

Author: keshav-space

docs/source/img/tutorial_remote_subscribe_package_update_add_purldb_remote_actor.jpg

@@ -25,6 +25,7 @@ you will find information on:
     :caption: Tutorial
 
     tutorial_getting_started
+    tutorial_remote_subscribe_package_update
 
 .. toctree::
     :maxdepth: 2

docs/source/img/tutorial_remote_subscribe_package_update_create_purldb_remote_actor_user.jpg

@@ -0,0 +1,94 @@
+.. _tutorial_remote_subscribe_package_update:
+
+Subscribe to Package Updates (Remote)
+=====================================
+
+
+In this tutorial, we will guide you through the step-by-step process of subscribing to
+package updates from a remote user. For this demo, we will subscribe to FederatedCode
+package updates in PurlDB. By the end of this tutorial, PurlDB will be able to subscribe
+to package updates and will receive ActivityPub streams for the activities of the subscribed
+packages.
+
+.. note::
+    This tutorial assumes that you have a working installation of FederatedCode.
+    If you don't, please refer to the :ref:`installation` page.
+
+
+Initial Setup (FederatedCode)
+-----------------------------
+
+#. Head over to :ref:`tutorial_getting_started` to perform the initial configuration of
+   FederatedCode after installation.
+
+#. Navigate to http://127.0.0.1:8000/admin/fedcode/remoteactor/add/ and add the ``purldb`` remote actor.
+   Populate the URL with http://127.0.0.1:8001/api/users/@purldb and set the username as ``purldb``.
+
+   .. image:: img/tutorial_remote_subscribe_package_update_add_purldb_remote_actor.jpg
+
+#. Navigate to http://127.0.0.1:8000/admin/fedcode/person/add/ to create the remote actor user.
+   For now, enter any value in the summary and public key fields, leave the user field empty,
+   and in the ``Remote actor`` dropdown, choose the one created in the previous step.
+
+   .. image:: img/tutorial_remote_subscribe_package_update_create_purldb_remote_actor_user.jpg
+
+
+Initial Setup (PurlDB)
+----------------------
+
+#. Follow the steps here to install PurlDB: https://aboutcode.readthedocs.io/projects/PURLdb/en/latest/getting-started/install.html#installation
+
+#. Add the FederatedCode ActivityPub server host to the ``.env`` file.
+
+    .. code-block:: bash
+       :caption: .env
+
+        FEDERATEDCODE_HOST_URL="http://127.0.0.1:8000"
+
+#. Subscribe to a PURL for updates. In this case, since we know that we have the
+   ``atlasboard`` package in our FederatedCode, we will subscribe to it.
+
+    .. code-block:: bash
+
+        python manage_purldb.py subscribe_package "pkg:npm/atlasboard"
+
+   On successful subscription, you will see this message:
+
+    .. code-block:: bash
+
+       {"status": "success", "message": "Successfully subscribed to package pkg:npm/atlasboard"}
+
+#. Navigate to http://127.0.0.1:8001/api/package_activity/ (Package updates received from FederatedCode ActivityPub will be available here).
+
+
+Update Package Scan (Git Repo)
+------------------------------
+
+Since we have subscribed to ``pkg:npm/atlasboard``, head over to
+https://github.com/<YOUR-GITHUB-USERNAME>/aboutcode-packages-npm-385/blob/main/npm/atlasboard/1.1.10/scancodeio.json,
+make some changes, and commit them.
+
+
+Run Sync and Federate (FederatedCode)
+-------------------------------------
+
+#. Run the following command to sync the changes made to the package scan in the Git repository
+
+    .. code-block:: bash
+
+        python manage.py sync sync_scancode_scans
+
+#. Run the following command to send activity updates to existing subscribers of the package
+
+    .. code-block:: bash
+
+        python manage.py federate
+
+Browse the Package Activity (PurlDB)
+------------------------------------
+
+Navigate to http://127.0.0.1:8001/api/package_activity/ to view the activity for the subscribed package.
+
+.. image:: img/tutorial_remote_subscribe_package_update_purldb_activity_endpoint.png
+
+