update readme, add screenshot

README.md

@@ -1,9 +1,45 @@
 # Digilines Control [digicontrol]
 
-[![luacheck](https://github.com/OgelGames/digicontrol/workflows/luacheck/badge.svg)](https://github.com/OgelGames/beacon/actions)
+[![luacheck](https://github.com/OgelGames/digicontrol/workflows/luacheck/badge.svg)](https://github.com/OgelGames/digicontrol/actions)
 [![License](https://img.shields.io/badge/License-MIT%20and%20CC%20BY--SA%204.0-green.svg)](LICENSE.md)
 
-Adds nodes to control the flow of digiline messages.
+## Table of Contents
+
+- [Overview](#overview)
+- [Nodes](#nodes)
+- [Dependencies](#dependencies)
+- [Installation](#installation)
+- [License](#license)
+
+## Overview
+
+This mod adds nodes to control the flow of digiline messages in various ways, and is designed to be a more streamlined replacement for [`digiline_routing`](https://github.com/numberZero/digiline_routing).
+
+![Overview Screenshot](screenshots/overview.png?raw=true "Overview Screenshot") 
+
+## Nodes
+
+- **Filter** - only lets messages with the correct channel pass through.
+- **Limiter** - limits the rate at which messages can pass through.
+- **Diode** - only lets messages pass through in one direction.
+- **Splitter** - splits messages into two branches, and stops messages going between the branches.
+- **Tri-Splitter** - same as Splitter, but splits into three branches.
+
+## Dependencies
+
+**Required**
+
+- `default` (included in [Minetest Game](https://github.com/minetest/minetest_game))
+- [`digilines`](https://github.com/minetest-mods/digilines)
+
+**Optional**
+
+- [`basic_materials`](https://gitlab.com/VanessaE/basic_materials)
+- `mesecons_materials` (included in [`mesecons`](https://github.com/minetest-mods/mesecons))
+
+## Installation
+
+Download the [master branch](https://github.com/OgelGames/digicontrol/archive/master.zip) or the [latest release](https://github.com/OgelGames/digicontrol/releases), or clone the repository using Git or the [GitHub Desktop](https://desktop.github.com/) app, and follow [these instructions](https://dev.minetest.net/Installing_Mods).
 
 ## License