Add a README for path.

pkg/path/lib/path.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// A comprehensive, cross-platform path manipulation library.
 library path;
 
 import 'dart:io' as io;
 
 /// An internal builder for the current OS so we can provide a straight
@@ skipping 13 matching lines @@
 ///     path.absolute('foo/bar.txt'); // -> /your/current/dir/foo/bar.txt
 String absolute(String path) => join(current, path);
 
 /// Gets the part of [path] after the last separator.
 ///
 ///     path.basename('path/to/foo.dart'); // -> 'foo.dart'
 ///     path.basename('path/to');          // -> 'to'
 ///
 /// Trailing separators are ignored.
 ///
-///     builder.dirname('path/to/'); // -> 'to'
+///     builder.basename('path/to/'); // -> 'to'
 String basename(String path) => _builder.basename(path);
 
 /// Gets the part of [path] after the last separator, and without any trailing
 /// file extension.
 ///
 ///     path.basenameWithoutExtension('path/to/foo.dart'); // -> 'foo'
 ///
 /// Trailing separators are ignored.
 ///
-///     builder.dirname('path/to/foo.dart/'); // -> 'foo'
+///     builder.basenameWithoutExtension('path/to/foo.dart/'); // -> 'foo'
 String basenameWithoutExtension(String path) =>
     _builder.basenameWithoutExtension(path);
 
 /// Gets the part of [path] before the last separator.
 ///
 ///     path.dirname('path/to/foo.dart'); // -> 'path/to'
 ///     path.dirname('path/to');          // -> 'to'
 ///
 /// Trailing separators are ignored.
 ///
@@ skipping 637 matching lines @@
     // If there is no dot, or it's the first character, like '.bashrc', it
     // doesn't count.
     if (lastDot <= 0) return [file, ''];
 
     return [file.substring(0, lastDot), file.substring(lastDot)];
   }
 
   _ParsedPath clone() => new _ParsedPath(
       style, root, new List.from(parts), new List.from(separators));
 }