Remove tags from list of missing documentation

docs/tutorial/conclusion.txt

@@ -4,7 +4,7 @@ Conclusion
 ==========
 
 This tutorial currently only covers a small (but important) part of Dulwich.
-It still needs to be extended to cover packs, tags, refs, reflogs and network
+It still needs to be extended to cover packs, refs, reflogs and network
 communication.
 
 Dulwich is abstracting much of the Git plumbing, so there would be more to