Add other download badges

[jermanuts]

the App store badge looks a bit off. Can you guys scale it? thanks.

[jermanuts]

or guess no need to scale lol

[sneurlax]

Looks good to me! Adds an App Store badge to the README.md, no other changes. Merge it!

[sneurlax]

Oh, the only minor issue with this is it's to main. We usually merge to staging then main. But these are nontechnical/documentation-only changes, so that's OK.

For future reference, if you are outside of the Cipher Stack organization, your PR test will always fail. So it's better to open a PR from some branch on your remote to some non-main and non-staging branch on ours and have one of us open the PR from that new bridge to staging--then tests will run with access to the secrets needed for certain features.

[jermanuts]

Can you look at #798, I couldn't fork Duo repo and accidently sent PR to this repo.

And add the App store badge for it too https://apps.apple.com/us/app/stack-duo-by-cypher-stack/id6446602017 and their F-Droid.

The base branch was changed.

[stokito]

The Get from F-Droid badge may be confusing because this is a link to a custom F-Droid repo, not the official. As I user I still prefer to use the official F-Droid repo because I know that they made a reproducible build and checked that the app is same as the app developers claim. Same confusion was mentioned in the #72 (comment)