Add Tern

[munzzyy]

Summary

Adds Tern to the Android App Store section, next to Obtainium. I'm its developer, so please weigh it like any other suggestion.

Checklist

• Entry uses the format - [Name](url) - description.
• New section is added to the Table of Contents (Contents): no new section here
• Project has a clear privacy / own-your-data policy: https://github.com/munzzyy/tern/blob/main/PRIVACY.md
• Project website loads no third-party trackers (only analytics from the Analytics section allowed)
• Source or repo link is provided
• License is stated
• Project is maintained, or flagged with 💀 if not