Add matcha to workspace

- Need this to be visible to pick up the rule in cross_platform.bzl

Change-Id: Ic049be40631368cea0c717d54a1c139a73709681
diff --git a/WORKSPACE b/WORKSPACE
index 9eb984c..e0a9784 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -7,6 +7,14 @@
 
 workspace(name = "lowrisc_opentitan")
 
+# We import this into the workspace to pick up a Bazel platform rule.
+# Be careful about importing anything else from here, it's not likely
+# to actually be something you want to do.
+local_repository(
+     name = "matcha",
+     path = "../matcha",
+)
+
 # CRT is the Compiler Repository Toolkit.  It contains the configuration for
 # the windows compiler.
 load("//third_party/crt:repos.bzl", "crt_repos")