win, doc: document per-drive current working dir

Add note to fs.md and path.md about Windows using per-drive current
working directory.

Fixes: nodejs#9378

doc/api/fs.md

@@ -94,6 +94,12 @@ Error: EISDIR: illegal operation on a directory, read
     <stack trace.>
 ```
 
+*Note:* On Windows Node follows the concept of per-drive working directory.
+This behavior can be observed when using a drive path without backslash, e.g.
+`fs.readdirSync('c:\\')` can potentially return different result than
+`fs.readdirSync('c:')`. For more information see
+[this MSDN page][MSDN-Rel-Path].
+
 ## WHATWG URL object support
 <!-- YAML
 added: v7.6.0
@@ -2835,6 +2841,7 @@ The following constants are meant for use with the [`fs.Stats`][] object's
 [FS Constants]: #fs_fs_constants_1
 [MDN-Date-getTime]: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date/getTime
 [MDN-Date]: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date
+[MSDN-Rel-Path]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247.aspx#fully_qualified_vs._relative_paths
 [Readable Stream]: stream.html#stream_class_stream_readable
 [Writable Stream]: stream.html#stream_class_stream_writable
 [inode]: https://en.wikipedia.org/wiki/Inode

doc/api/path.md

@@ -54,6 +54,11 @@ path.posix.basename('/tmp/myfile.html');
 // Returns: 'myfile.html'
 ```
 
+*Note:* On Windows Node follows the concept of per-drive working directory.
+This behavior can be observed when using a drive path without backslash, e.g.
+`path.resolve('c:\\')` can potentially return different result than
+`path.resolve('c:')`. For more information see [this MSDN page][MSDN-Rel-Path].
+
 ## path.basename(path[, ext])
 <!-- YAML
 added: v0.1.25
@@ -550,3 +555,4 @@ of the `path` methods.
 [`path.posix`]: #path_path_posix
 [`path.sep`]: #path_path_sep
 [`path.win32`]: #path_path_win32
+[MSDN-Rel-Path]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247.aspx#fully_qualified_vs._relative_paths