add the SHA-256 hash of signing certificate in the README

[stenech]

Checklist

• I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
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• This issue contains only one feature request.
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Feature description

Hi!,
Great app, using it often!
Could you please add the SHA-256 hash of signing certificate in the README so that one can verify the APK?
Also, it's extra but it might help others if you also posted it on a social media so that in case your github got compromised, others can still verify from the SM post 😉
Thank you!

Why do you want this feature?

People downloading directly from source (Github) need to verify the APK via apps like AppVerifier

Additional information

No response