add usage

README.md

@@ -9,6 +9,20 @@ The fish nibble on clammy fingers, and the machine sings me a lullaby:
 a dream within a dream of knowledge only it possesses.
 ```
 
+## Usage
+
+This is extremely early stage, but you’ll need `OSProcess` support in Pharo. To
+get it, run:
+
+```
+Gofer new
+	squeaksource: 'OSProcess';
+	package: 'OSProcess';
+	load.
+```
+
+in a playground.
+
 <hr/>
 
 Have fun!