Fix broken link

Use an absolute path for the TCPRoute spec. The current relative path
attempts to load /tcp/spec/#networking.x-k8s.io/v1alpha1.TCPRoute, but
the spec actually lives at /spec/#networking.x-k8s.io/v1alpha1.TCPRoute

Author: Travis Raines

site-src/tcp.md

@@ -1,5 +1,5 @@
 Gateway API is designed to work with multiple protocols.
-[TCPRoute](spec/#networking.x-k8s.io/v1alpha1.TCPRoute) is one such route which
+[TCPRoute](/spec/#networking.x-k8s.io/v1alpha1.TCPRoute) is one such route which
 allows for managing TCP traffic.
 
 In this example, we have one Gateway resource and two TCPRoute resources that