docs(readme): Add features and installation sections

README.md

@@ -5,3 +5,17 @@ A Nightscout plugin for the Elgato Stream Deck.
 <p align="center">
   <img src="./assets/preview.svg" title="Nightscout Preview Image" align="center" width="100"/>
 </p>
+
+## Features
+
+- Displays current blood sugar reading, change since last reading, and an arrow
+- Supports mg/dL and mmol/L
+- Supports Nightscout API tokens
+- Only requests new data when a new reading should be available, which gives timely data while also conserving battery life
+
+## Installation
+
+### Manual Installation
+
+- Download the latest plugin release [here](https://github.com/gabe565/streamdeck-nightscout/releases/latest)
+- Open downloaded `.sdplugin` file. It will be automatically installed to your Stream Deck application.