add a link to remote trybot guide to test_that doc

BUG=b:29371718
TEST=None

Change-Id: I9a447d069be0b5499b2d08a2a49518eb203b9b50
Reviewed-on: https://chromium-review.googlesource.com/353025
Reviewed-by: Simran Basi <sbasi@chromium.org>
Tested-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/docs/test-that.md b/docs/test-that.md
index aa23cd4..164ca18 100644
--- a/docs/test-that.md
+++ b/docs/test-that.md
@@ -61,7 +61,10 @@
 running tests against a specified host. The keyword :lab: is used as
 test\_that's REMOTE argument, and the -i/--build argument is required, and takes
 a trybot, paladin, or canary build number. To learn how to build a trybot image
-with a new test that you're iterating on, see "dynamic suite" codelab.
+with a new test that you're iterating on, see "dynamic suite" codelab or the
+[Chromium OS Remote
+Trybots](https://sites.google.com/a/chromium.org/dev/chromium-os/build/using-remote-trybots)
+guide.
 
 For instance: