Added warning when pages dir is not present (#14)

* Added warning when pages dir is not present and a special one if it exists as a sibling of the project root

* Added requested copy changes

bin/next-dev

 #!/usr/bin/env node
-
-import { resolve } from 'path'
+import { resolve, join } from 'path'
 import parseArgs from 'minimist'
 import Server from '../server'
 import build from '../server/build'
+import { exists } from 'mz/fs'
 
 const argv = parseArgs(process.argv.slice(2), {
   alias: {
@@ -23,6 +23,15 @@ build(dir)
   const srv = new Server({ dir, dev: true })
   await srv.start(argv.port)
   console.log('> Ready on http://localhost:%d', argv.port)
+
+  // Check if pages dir exists and warn if not
+  if (!await exists(join(dir, 'pages'))) {
+    if (await exists(join(dir, '..', 'pages'))) {
+      console.warn('> No `pages` directory found. Did you mean to run `next` in the parent (`../`) directory?')
+    } else {
+      console.warn('> Couldn\'t find a `pages` directory. Please create one under the project root')
+    }
+  }
 })
 .catch((err) => {
   console.error(err)