Social preview image for repositories

[mueller-ma]

When sharing a link to a website the used application, e.g. Signal messenger, might download and display additional information for this link by fetching the Open Graph tags.
GitHub allows to set a preview images for each repository, which can be done in the repo settings, e.g. https://github.com/openhab/openhab-android/settings.
For the Android repo I set https://github.com/openhab/openhab-android/blob/master/fastlane/metadata/android/en-US/images/featureGraphic.png as preview, which could be done for other repos as well.