fix(docs): add basic usage instructions

README.md

@@ -1,3 +1,43 @@
 # midi-mixer-cli
 
 A CLI tool to help with the packaging and distribution of MIDI Mixer plugins.
+
+```
+Usage: midi-mixer [options] [command]
+
+A CLI tool to help with the packaging and distribution of MIDI Mixer plugins.
+
+Options:
+  -V, --version   output the version number
+  -h, --help      display help for command
+
+Commands:
+  pack [options]  Package a plugin ready for distribution.
+  help [command]  display help for command
+```
+
+## Packaging plugins
+
+Use the `midi-mixer pack` command to package a built plugin in to a `.midiMixerPlugin` file ready for distribution.
+
+```
+Usage: midi-mixer pack [options]
+
+Package a plugin ready for distribution.
+
+Options:
+  -m --manifest <path>  target plugin.json file
+  -h, --help            display help for command
+```
+
+```
+> midi-mixer pack
+
+  √ Finding plugin manifest
+  √ Verifying manifest shape
+  √ Verifying manifest targets
+  √ Package
+  √ Finalising
+```
+
+For a plugin with the name `foo` on version `1.0.0`, the plugin file generated would be called `foo-1.0.0.midiMixerPlugin`.