Add readme.

README.md

@@ -1,2 +1,28 @@
 # ButlerBotNG
 
+## Installation
+
+```bash
+$ npm install
+```
+
+## Usage
+
+1. Create `.env` (see `example.env`) and populate with all necessary details.
+2. Register slash commands.
+
+```bash
+$ npm run register-slash-commands
+```
+
+3. Run ButlerBot.
+
+```bash
+$ npm run start
+```
+
+## Development
+
+All commands are dynamically loaded at runtime, and are stored in `src/commands/[CATEGORY]/[NAME].js`.
+To add a new command, just create a new .js file. It must export a `data` object and `execute` promise. See existing commands for an example.
+Remember to re-register slash commands using `npm run register-slash-commands` if adding a new command, or modifying an existing command's parameters.