Versions docs

docs/VERSIONS.md

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+## Am I running the latest released version?
+
+Since version 23.01.14 PiAlert uses a simple timestamp-based version check to verify if a new version is available. You can check the [current and past releases here](https://github.com/jokob-sk/Pi.Alert/releases), or have a look at what I'm [currently working on](https://github.com/jokob-sk/Pi.Alert/issues/138). 
+
+If you are not on the latest version, the app will notify you, that a new released version is avialable the following way:
+
+### 📧 Via email on a notification event
+
+If any notification occurs and an email is sent, the email will contain a note that a new version is available. See the sample email below:
+
+![Sample email if a new version is available](/docs/img/VERSIONS/new-version-available-email.png)
+
+### 🆕 In the UI
+
+In the UI via a notification Icon and via a custom message in the Maintenance section.
+
+![UI screenshot if a new version is available](/docs/img/VERSIONS/new-version-available-maintenance.png)
+
+For a comparison, this is how the UI looks like if you are on the latest stable image:
+
+![UI screenshot if on latest version](/docs/img/VERSIONS/latest-version-maintenance.png)
+
+## Implementation details
+
+During build a [/home/pi/pialert/front/buildtimestamp.txt](https://github.com/jokob-sk/Pi.Alert/blob/092797e75ccfa8359444ad149e727358ac4da05f/Dockerfile#L44) file is created. The app then periodically checks if a new release is available with a newer timestamp in GitHub's rest-based JSON endpoint (check the `def isNewVersion():` method in `pialert.py` for details).