Add README and license

LICENSE

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+Copyright 2020 Ibiyemi Abiodun
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+# Reaction Bot
+
+Facebook Messenger and iMessage have features that allow you to react to
+messages with emojis - it's an inline, low-key way to acknowledge a message when
+you don't have anything else to say. However, this feature is still missing from
+Telegram, so this bot serves as a sort of polyfill.
+
+## How to use it (for Telegram users)
+
+- Add [@reaxnbot](https://t.me/reaxnbot) to a group chat
+- Reply to any message with the `/r` command directed at `@reaxnbot` (you can just type `/r` and it should just work)
+- `@reaxnbot` responds with an empty message with emoji buttons, and anyone can
+  tap them to react
+
+![example showing reaxnbot in action](doc/example-1.png)
+
+- If you don't want your chat littered with `/r`s, then give the bot permissions
+  to delete messages and it will automatically delete the `/r` messages.
+
+## How to use it (for developers)
+
+- Obtain a bot token from the [BotFather](https://t.me/botfather)
+- `TELOXIDE_TOKEN=<your token here> cargo run`
+
+## EAQ (Easily anticipated questions)
+
+> Why does this bot have the ability to read all messages in my group chat?
+
+Due to the [way the Telegram Bot API works](https://core.telegram.org/bots/faq#what-messages-will-my-bot-get), replying to a message with a bot command doesn't let the bot see which message you're replying to. This bot would be a lot less useful if it wasn't clear which message the reaction was for, so this is a no-go.
+
+The bot completely ignores messages that are not commands directed at it, and
+does not read the contents of the messages you use it to react to.
+
+> I don't want this bot to delete my `/r` messages. / I don't trust this bot not to delete anything else.
+
+Then don't give the bot deletion permissions.
+
+## License
+
+This code is MIT licensed. Copyright &copy; 2020 Ibiyemi Abiodun.