doc,fs: document value of stats.isDirectory on symbolic links

PR-URL: #27413
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Antoine du Hamel <[email protected]>

Author: coderaiser

Diff for: doc/api/fs.md

@@ -826,6 +826,10 @@ added: v0.1.10
 
 Returns `true` if the `fs.Stats` object describes a file system directory.
 
+If the `fs.Stats` object was obtained from [`fs.lstat()`][], this method will
+always return `false`. This is because [`fs.lstat()`][] returns information
+about a symbolic link itself and not the path it resolves to.
+
 ### `stats.isFIFO()`
 <!-- YAML
 added: v0.1.10