[luciexe] Clear up documentation around State.Log stream closure

Change-Id: I5ab6e9f00ed5e2165588753fd5b15579ce78162f
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/4060195
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Michael Knyszek <mknyszek@google.com>
diff --git a/luciexe/build/state.go b/luciexe/build/state.go
index c6e54cc..a7d3300 100644
--- a/luciexe/build/state.go
+++ b/luciexe/build/state.go
@@ -159,7 +159,7 @@
 
 // Log creates a new build-level line-oriented text log stream with the given name.
 //
-// You must close the stream when you're done with it.
+// The stream will close when the state is End'd.
 func (s *State) Log(name string, opts ...streamclient.Option) io.Writer {
 	var ret io.WriteCloser