Add `topics` to  `pubspec.yaml` (#165)

diff --git a/pubspec.yaml b/pubspec.yaml
index b6e2a91..91bbca2 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -6,6 +6,9 @@
   web.
 repository: https://github.com/dart-lang/path
 
+topics:
+ - file-system
+
 environment:
   sdk: ^3.0.0