docs: process.memoryUsage returns memory usage measured in bytes

doc/api/process.markdown

@@ -280,7 +280,8 @@ What platform you're running on. `'linux2'`, `'darwin'`, etc.
 
 ### process.memoryUsage()
 
-Returns an object describing the memory usage of the Node process.
+Returns an object describing the memory usage of the Node process
+measured in bytes.
 
     var util = require('util');