docs(readme): add usage

README.md

@@ -1,3 +1,23 @@
 # cli
 
-The command line interface for telegram.
+The command line interface for telegram.
+
+```console
+$ go install github.com/gotd/cli/cmd/tg@latest
+```
+
+## Usage
+
+First, initialize configuration (currently only for bots)
+
+```console
+$ tg init --app-id APP_ID --app-hash APP_HASH --token BOT_TOKEN
+```
+
+This will create config in `gotd` subdirectory of default config directory, for example `~/.config/gotd/gotd.cli.yaml`.
+
+Now you can issue commands to control your bot.
+For example, you can send `Hello world` to `@gotd_test`:
+```bash
+$ tg send --peer gotd_test "Hello world"
+```