Update README

# K-9 Mail

[![Latest release](https://img.shields.io/github/release/k9mail/k-9.svg?style=flat-square)](https://github.com/k9mail/k-9/releases/latest)

[![Latest beta release](https://img.shields.io/github/v/release/k9mail/k-9.svg?include_prereleases&style=flat-square)](https://github.com/k9mail/k-9/releases)

[![Latest release](https://img.shields.io/github/release/thundernest/k-9.svg?style=flat-square)](https://github.com/thundernest/k-9/releases/latest)

[![Latest beta release](https://img.shields.io/github/v/release/thundernest/k-9.svg?include_prereleases&style=flat-square)](https://github.com/thundernest/k-9/releases)

K-9 Mail is an open-source email client for Android.

- [Google Play](https://play.google.com/store/apps/details?id=com.fsck.k9)

- [F-Droid](https://f-droid.org/repository/browse/?fdid=com.fsck.k9)

- [Github Releases](https://github.com/k9mail/k-9/releases)

- [Github Releases](https://github.com/thundernest/k-9/releases)

You might also be interested in becoming a [tester](https://forum.k9mail.app/t/how-do-i-become-a-beta-tester/68) to get an early look at new versions.

## Release Notes

Check out the [Release Notes](https://github.com/k9mail/k-9/wiki/ReleaseNotes) to find out what changed

Check out the [Release Notes](https://github.com/thundernest/k-9/wiki/ReleaseNotes) to find out what changed

in each version of K-9 Mail.

Thank you for contributing! If you're unfamiliar with the code, 

start by reading the [developer documentation](docs/DESIGN.md)

Please fork this repository and contribute back using [pull requests](https://github.com/k9mail/k-9/pulls).

Please fork this repository and contribute back using [pull requests](https://github.com/thundernest/k-9/pulls).

Any contributions, large or small, major features, bug fixes, unit/integration tests are welcomed and appreciated

but will be thoroughly reviewed and discussed.

Please make sure you read the [Code Style Guidelines](https://github.com/k9mail/k-9/wiki/CodeStyle).

Please make sure you read the [Code Style Guidelines](https://github.com/thundernest/k-9/wiki/CodeStyle).

## Communication

Aside from discussing changes in [pull requests](https://github.com/k9mail/k-9/pulls) and

[issues](https://github.com/k9mail/k-9/issues) we use the following communication services:

Aside from discussing changes in [pull requests](https://github.com/thundernest/k-9/pulls) and

[issues](https://github.com/thundernest/k-9/issues) we use the following communication services:

- Matrix: [#k9mail:matrix.org](https://matrix.to/#/#k9mail:matrix.org)

- Matrix: [#k9mail:matrix.org](https://matrix.to/#/#tb-android:mozilla.org)

- IRC: [#k9mail on Libera Chat](https://web.libera.chat/#k9mail)

- [Developer mailing list](https://groups.google.com/forum/#!forum/k-9-dev)