Support Hugo extended (#65)

* wip: Support Hugo extended

* fallback support, update readme.md

* fixup! wip: Support Hugo extended

lib/install.js

@@ -1,7 +1,26 @@
+const path = require('path');
 const bin = require('./');
 const log = require('logalot');
 
-bin.run(['version'])
+function getProjectRoot() {
+  // projectRoot on postinstall could be INIT_CWD introduced in npm>=5.4
+  // see: https://github.com/npm/npm/issues/16990
+  const initCwd = process.env.INIT_CWD;
+  if (initCwd) {
+    return initCwd;
+  }
+  // Fallback of getting INIT_CWD
+  const cwd = process.cwd();
+  const paths = cwd.split(path.sep);
+  // If process.cwd end with 'node_modules/*' then get the dependent root directory,
+  // otherwise returns cwd (ordinary it will be the postinstall process of hugo-bin itself).
+  if (paths.length > 1 && paths[paths.length - 2] === 'node_modules') {
+    return path.resolve('../../', cwd);
+  }
+  return cwd;
+}
+
+bin(getProjectRoot()).run(['version'])
 .then(() => {
   log.success('Hugo binary is installed successfully');
 })