Merge pull request #240 from owenv/readme-patch

Add trunk snapshot requirement to the README

Author: owenv

README.md

@@ -11,6 +11,8 @@ The `swift-driver` project is a new implementation of the Swift compiler driver
 
 ## Getting Started
 
+**Note:** Currently, swift-driver is only compatible with trunk development snapshots from [swift.org](https://swift.org/download/#snapshots).
+
 The preferred way to build `swift-driver` is to use the Swift package manager:
 
 ```