feat: create initial README for supersim

README.md

@@ -1,2 +1,22 @@
-# supersim
-Local Multi-L2 Development Environment
+# Supersim
+Supersim is a local Multi-L2 Development Environment.
+
+## Overview
+Supersim allows developers to start multiple local Layer 2 chains with one command, and coordinates message passing and asset transfer between these chains.
+
+Supersim is a lightweight tool that simulates an interoperable Superchain environment locally. It does not require a complicated devnet setup and is run using cli commands with configuration options that fall back to sensible defaults if they are not specified. 
+
+## Modes
+
+Each L2 chain is an instance of [anvil](https://book.getfoundry.sh/reference/anvil/).
+
+### Vanilla Mode
+Brings up one L1 chain and 2 L2 chains with the appropriate OP Stack contracts already deployed, allowing you to locally test against the latest OP Stack features.
+
+To run vanilla mode simply run:
+TODO: insert command
+
+### Forked Mode
+
+## Examples
+TODO