Mailcow: Add README.
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+= Mailcow on Kubernetes
+Matthias Andreas Benkard
+:experimental:
+:data-uri:
+:sectnums:
+:toc:
+:stem:
+:toclevels: 2
+:icons: font
+:source-highlighter: prettify
+
+== Description
+
+This directory contains a distribution of https://mailcow.github.io/mailcow-dockerized-docs/[*Mailcow*]
+that you can run in a https://matthias.benkard.de/posts/814[*Kata container*] as part of a *Kubernetes cluster*.
+
+The main artifact provided is a Docker image, meant to run in a Kata container, which embeds its own
+https://www.docker.com[Docker daemon] and copies of https://docs.docker.com/compose/[docker-compose] and a very slightly patched
+https://github.com/mailcow/mailcow-dockerized/[mailcow-dockerized].
+
+== Usage
+
+=== Building the Docker image
+
+The main Docker image that you can run in the cluster is defined in link:default.nix[].
+To build it, you can either go through the regular procedure of
+https://nixos.org/guides/building-and-running-docker-images.html[building Docker images with Nix]
+or make use of the top-level link:../Makefile[Makefile]:
+
+[source,shell script]
+----
+make mailcow.load
+----
+
+After building and loading the image, push it to the registry of your choice.
+
+=== Deploying to Kubernetes
+
+First, create a *configuration file* as explained in the https://mailcow.github.io/mailcow-dockerized-docs/i_u_m_install/[Mailcow installation howto] and deploy the configuration as a *Kubernetes secret*:
+
+[source,shell script]
+----
+kubectl create secret generic mailcow-secrets \
+ --from-file=mailcow.conf=src/mailcow-dockerized/mailcow.conf
+----
+
+You can then use the provided link:mailcow.yaml[] file to perform the *deployment*.
+Be sure to change the *image name* to the image you built above.
+You probably also want to adjust the *namespace* unless a namespace named `mulk` makes sense to you.
+
+=== Updating Mailcow
+
+Updating should usually be as easy as *synchronizing* the link:src/mailcow-dockerized/[] subtree with *upstream* and then <<Building the Docker image,rebuilding the image>>.
+
+To synchronize the subtree, use `git subtree`:
+
+[source,shell script]
+----
+git subtree pull \
+ --prefix=mailcow/src/mailcow-dockerized \
+ https://github.com/mailcow/mailcow-dockerized.git \
+ master
+----