doc: document DistGit cleanup

Closes: fedora-copr#3188

doc/developer_documentation/architecture.rst

@@ -1,3 +1,5 @@
+.. _architecture:
+
 Basic Copr build process / Architecture diagram
 -----------------------------------------------
 

doc/maintenance/dist-git.rst

@@ -0,0 +1,31 @@
+.. _maintaining_distgit:
+
+DistGit VM maintenance
+======================
+
+The Copr DistGit machine serves as a "proxy" middle-man between the actual source
+code location and our farm of builders.  See :ref:`architecture` for more
+info.  There's no data-consistency promise regarding Copr's DistGit data;
+our primary goal is to ensure effective Copr Builds.  Consequently, we
+only strive to keep the "proxy" sources for the **existing packages**
+within still **existing Copr projects**.
+
+Cleaning up DistGit
+-------------------
+
+Copr is a place where CI is done frequently, leading to the generation of
+a significant amount of "source" data.  Often, each CI build produces a
+different tarball that is uploaded and stored on the Copr DistGit machine.
+Copr projects are also often short-lived (e.g., Packit).  This
+necessitates Copr to conduct regular DistGit cleanup to prevent the source
+data consumption from quickly exploding.
+
+Currently, we have two house-cleaning procedures for DistGit:
+
+1. `Cleaning up sources for outdated builds <https://github.com/fedora-copr/copr/blob/main/dist-git/run/dist-git-clear-tarballs.py>`_
+
+2. `Cleaning up old repositories and sources for deleted Copr projects <https://github.com/fedora-copr/copr/blob/main/dist-git/run/prune-dist-git.py>`_
+
+Both of these procedures are not enabled "by default" on every Copr
+deployment.  However, Fedora Copr has automated these scripts using cron.
+

doc/maintenance_documentation.rst

@@ -56,3 +56,4 @@ This section contains information about maintenance topics. You may also be inte
    email_templates
    Sending notifications and removing data from outdated chroots <how_to_delete_outdated_chroots>
    Monitoring the service <maintenance/monitoring>
+   Maintaining DistGit machine <maintenance/dist-git>