doc: clarify that path on windows accepts / and \

Fixes: https://github.com/nodejs/node/issues/6520
PR-URL: https://github.com/nodejs/node/pull/8291
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/api/path.md

@@ -261,10 +261,13 @@ path.isAbsolute('.')        // false
 On Windows:
 
 ```js
-path.isAbsolute('//server')  // true
-path.isAbsolute('C:/foo/..') // true
-path.isAbsolute('bar\\baz')  // false
-path.isAbsolute('.')         // false
+path.isAbsolute('//server')    // true
+path.isAbsolute('\\\\server')  // true
+path.isAbsolute('C:/foo/..')   // true
+path.isAbsolute('C:\\foo\\..') // true
+path.isAbsolute('bar\\baz')    // false
+path.isAbsolute('bar/baz')     // false
+path.isAbsolute('.')           // false
 ```
 
 A [`TypeError`][] is thrown if `path` is not a string.
@@ -509,6 +512,10 @@ added: v0.11.15
 The `path.win32` property provides access to Windows-specific implementations
 of the `path` methods.
 
+*Note*: On Windows, both the forward slash (`/`) and backward slash (`\`)
+characters are accepted as path delimiters; however, only the backward slash
+(`\`) will be used in return values.
+
 [`path.posix`]: #path_path_posix
 [`path.win32`]: #path_path_win32
 [`path.parse()`]: #path_path_parse_path