update update documentation

How-to-update-openwebrx.md

@@ -1,3 +1,49 @@
-Just open a terminal and make
+The steps to update an existing installation of OpenWebRX depend on the method of installation that was used for the
+initial installation.
 
-`sudo apt update;sudo apt upgrade`
+# Installations using the OpenWebRX repositories (including Raspberry Pi images)
+
+When using the OpenWebRX repository, the update procedure is the same as for other software packages on the system.
+
+The simplest way typically involves these commands:
+
+```
+sudo apt-get update
+sudo apt-get install openwebrx
+```
+
+Other options, such as `apt-get upgrade` or `apt-get dist-upgrade` should work as well. Please consult your package
+manager documentation for details and differences.
+
+# Installations using Docker
+
+The typical update procedure for a docker container is to pull the new image from the Docker hub and then re-creating
+the container, usually with the same parameters.
+
+This helper script can perform these steps whenever you call it. You may need to modify the parameters to the
+`docker run` command to suit your needs:
+
+```
+#!/usr/bin/env bash
+set -euo pipefail
+
+TAG=stable
+
+docker pull jketterl/openwebrx:${TAG}
+docker stop openwebrx || true
+docker rm openwebrx || true
+docker run --name openwebrx -d --restart=unless-stopped --device /dev/bus/usb --tmpfs=/tmp/openwebrx -p 8073:8073 -v openwebrx-config:/etc/openwebrx -v openwebrx-settings:/var/lib/openwebrx jketterl/openwebrx:${TAG}
+```
+
+It also allows you to switch between different tags (e.g. from `stable` to `latest`) by simply changing the `TAG` variable.
+
+# Manual installation method
+
+Installations that have been set up according to the [manual installation procedure](https://github.com/jketterl/openwebrx/wiki/Manual-Package-installation-(including-digital-voice))
+will need to re-visit the instructions and manually update the components of the installation individually. Most steps
+of the procedure should give you a new version by simply repeating them.
+
+OpenWebRX itself can be updated using the `git` version control software. For most cases, `git pull` should give you the
+latest version. You may need to switch to a different branch or tag using `git checkout` depending on your intentions.
+You may additionally need to resolve potential conflicts that may arise if any of the files of the checkout were
+modified.