readme: mention newlines and cloning on Windows

Author: Conduitry

README.md

@@ -41,6 +41,11 @@ cd svelte
 npm install
 ```
 
+> Many tests depend on newlines being preserved as `<LF>`. On Windows, you can ensure this by cloning with:
+> ```bash
+> git -c core.autocrlf=false clone https://github.com/sveltejs/svelte.git
+> ```
+
 To build the compiler, and all the other modules included in the package:
 
 ```bash