Update ARCHITECTURE.md

Fix broken link (drive-by as I'm reading)
diff --git a/doc/ARCHITECTURE.md b/doc/ARCHITECTURE.md
index f0650f5..c72b4a5 100644
--- a/doc/ARCHITECTURE.md
+++ b/doc/ARCHITECTURE.md
@@ -63,7 +63,7 @@
 
 ## Path encoding
 
-See [Path segment encoding](./doc/pathseg.md) document.
+See [Path segment encoding](./pathseg.md) document.
 
 
 ## Intermediary layers