initial fastlane structures from IzzyOnDroid

[IzzySoft]

this PR provides you with a "fastlane starter package" – to give it into your hands to define how your app is presented, and make it easy to keep descriptions & graphics in sync with your development. Some notes to sum them up in a place easy to find for you:

• the IzzyOnDroid Fastlane Documentation can guide you with maintaining the structures here
• take special care for limits, e.g. per-release changelogs can have max 500 chars, full_description.txt max 4,000 chars, graphics must have specific aspect ratios etc.
• you can have "bigger graphics" here; the IoD updater takes care to resize/optimize them as needed
• for the full_description.txt here I've used HTML compressed into a single line, to prevent the fdroid software converting each line break to a <br>. The tags used for this are supported by F-Droid.org as well, and to my knowledge even by PlayStore.
• whenever you add a new "type" of metadata that has not been there before (e.g. the first changelog, a featureGraphic if it wasn't yet present), please let us know so we can check and enable it.
• Details on all this in the linked documentation.
• Once merged, your changes will be synced whenever a new release is pulled in here – to make sure it stays up-to-date with the app itself.
• Should you have questions, be welcome to ask 😉

If you wonder: xray-plugin is available at IzzyOnDroid. We publish the APKs built and signed by their resp. developers, after having passed them through additional screening. Which brings me to a question: APKs were attached to releases in the past, now there are no releases anymore at all. Will they return?

Related issue: #9 (simply add screenshots as JPG or PNG by placing the files into fastlane/metadata/android/en-US/phoneScreenshots/. F-Droid will pick them up from there automatically (and IzzyOnDroid after we've been notified and cross-checked formatting).

And now: Enjoy!

[IzzySoft]

@teddysun any chance to get this merged? Would help us at IzzyOnDroid as well 🙏

[IzzySoft]

@teddysun you still there?