doc: clarify that path.isAbsolute on windows accepts / and \

Fixes: #6520

Author: jasnell

doc/api/path.md

@@ -261,12 +261,18 @@ 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
 ```
 
+*Note*: On Windows, the `path.isAbsolute()` method will accept both forward
+slash (`/`) and backwards slash (`\`) characters as path delimiters.
+
 A [`TypeError`][] is thrown if `path` is not a string.
 
 ## path.join([path[, ...]])