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 😉

And now: Enjoy!

PS: KernelSU at IzzyOnDroid

[IzzySoft]

@tiann any chance to get this merged? As we need to move on with our repo reorg at IzzyOnDroid, it would help us a lot. Thanks in advance!

[IzzySoft]

We're now about to finalize our repo reorg, and thus would very much appreciate if you could merge this PR, so description & graphics can be kept in sync, @tiann 🙏

For motivation, here again the monthly installs/updates from IzzyOnDroid:

Worth to be properly supported?

[tiann]

Sorry for the delay, I’ve been a bit tied up lately.

[IzzySoft]

Thanks a lot 🤗 All set at our end now as well, so any future changes you might make, should be synchronized automatically whenever a new release is being pulled in. Should you add screenshots, a featureGraphic, or per-release changelogs one day, please let us know, so we can check and activate them at our end as well.