Split README into a bunch of files in docs/

docs/uninstalling.md

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+# Uninstalling
+
+**Note**: If you have some trouble with your installation configuration, you can just [re-run the playbook](installing.md) and it will try to set things up again. You don't need to uninstall and install fresh.
+
+However, if you've installed this on some server where you have other stuff you wish to preserve, and now want get rid of Matrix, it's enough to do these:
+
+- ensure all Matrix services are stopped (`systemctl stop 'matrix*'`)
+
+- delete the Matrix-related systemd .service files (`rm -f /etc/systemd/system/matrix*`) and reload systemd (`systemctl daemon-reload`)
+
+- delete all Matrix-related cronjobs (`rm -f /etc/cron.d/matrix*`)
+
+- delete some helper scripts (`rm -f /usr/local/bin/matrix*`)
+
+- delete some cached Docker images (or just delete them all: `docker rmi $(docker images -aq)`)
+
+- delete the Docker network: `docker network rm matrix`
+
+- uninstall Docker itself, if necessary
+
+- delete the `/matrix` directory (`rm -rf /matrix`)