chore: README.md (#3)

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README.md

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+# sessions
+
+A browser extension aiming to simplify coplaying in [Tribal Wars](https://www.tribalwars.net/en-dk/). Coplayers can finally play together via a browser!
+
+## Getting started
+
+### Development
+
+#### Setting up the environment
+
+Prerequisites:
+
+1. **Node.js** (LTS)
+2. **IDE/Code editor** (e.g. WebStorm, VSCode, vim, neovim)
+3. **web-ext** (``yarn global add web-ext``)
+4. **backend** (such as [this one](https://gitea.dwysokinski.me/twhelp/sessions))
+5. **Chromium-based browser** (e.g. Chromium, Vivaldi, Brave)
+
+```shell
+# start a dev server
+yarn watch
+
+# launch a browser (e.g. Chromium)
+yarn run:chromium
+```
+
+## FAQ
+
+1. What data are sent to the backend? - Only sid (session identifier). Sid is [encrypted/decrypted on the client side](./src/crypto.ts).
+
+## License
+
+Distributed under the MIT License. See ``LICENSE`` for more information.
+
+## Contact
+
+Dawid Wysokiński - [contact@dwysokinski.me](mailto:contact@dwysokinski.me)