Update README

Author: neonichu

README.md

@@ -2,13 +2,25 @@
 
 Allows using `libjvm` in other Swift packages.
 
+Note: this has only been tested on OS X 10.11 right now and will require
+different paths if used on any other operating system.
+
 ## Usage
 
 ```swift
+import PackageDescription
+
 let package = Package(
     name: "example",
     dependencies: [
         .Package(url: "https://github.com/neonichu/CJavaVM", majorVersion: 1)
     ]
 )
 ```
+
+Build your dependent packages somewhat like this:
+
+```bash
+JVM_LIBRARY_PATH=/Library/Java/JavaVirtualMachines/jdk1.8.0_45.jdk/Contents/Home/jre/lib/server
+swift build -Xlinker -L$(JVM_LIBRARY_PATH) -Xlinker -rpath -Xlinker $(JVM_LIBRARY_PATH)
+```