lntest: Add doc.go with package documentation.

lntest/doc.go

@@ -0,0 +1,10 @@
+/*
+Package lntest provides testing utilities for the lnd repository.
+
+This package contains infrastructure for integration tests that launch full lnd
+nodes in a controlled environment and interact with them via RPC. Using a
+NetworkHarness, a test can launch multiple lnd nodes, open channels between
+them, create defined network topologies, and anything else that is possible with
+RPC commands.
+*/
+package lntest