Add privacy policy

PRIVACY.md

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+# Privacy Policy
+
+## What data the Gotify app might collect, store and process
+
+The app only records data strictly necessary for the app to function. This
+includes for example the app settings and images caches. The app does not
+include any advertisement libraries or any 3rd party tracking (analytics) code,
+such as Google Analytics.
+
+gotify/android needs to be connected to a gotify/server for full functionality
+and the app may share data with this server. After the app is launched, you
+will be prompted to set a gotify/server URL. You, as a user, are responsible
+for verifying that you can trust this server instance.
+
+For best privacy, you should host gotify/server yourself, as then only you have
+access to your data.
+
+## What app data other parties might collect, store and process
+
+If you have activated "backup & reset" in your phone settings (Settings /
+Backup & Reset / Back up my data), you should be aware that Android itself will
+periodically save a copy of your phone’s data in Google’s servers. For more
+information, see [Google's privacy policy](https://policies.google.com).
+
+## What data the Gotify team may have access to
+
+The developers of Gotify do **not** have access to any of your information,
+except when you
+
+- actively share debugging information (either via email using the 'Crash
+  Report' function, or via the Android crash reporting functionality of
+  Google):
+  - device type
+  - Android version
+  - Gotify version
+  - Error messages
+- actively share a review in the Google Play store:
+  - public profile information
+  - Gotify version
+  - device type
+  - device language
+  - Android version
+
+## Updates of this Privacy Policy
+
+The developers may update this policy in the future. It is advisable to check
+the policy periodically for any changes. Changes to this Privacy Policy are
+effective when they are made on this document.
+
+This Privacy Policy was last updated on 2022-06-30, If you have questions, open
+an issue on GitHub.