Add a package.json so that npm can install this.

package.json

@@ -0,0 +1,5 @@
+{ "name" : "nvm"
+, "version" : "0.0.2"
+, "bin" : { "nvm" : "./nvm.sh" }
+, "author" : "Tim Caswell <tim@creationix.org>"
+}