README.txt: Add README describing what this repo is for.

Shows how to run the tests this repo was created for.

BUG=None
TEST=None

Change-Id: I118343d6d86f87755a65cf89c2c5ccb8ab592342
Reviewed-on: https://chromium-review.googlesource.com/291351
Reviewed-by: Matthew Sartori <msartori@chromium.org>
Commit-Queue: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
diff --git a/README.txt b/README.txt
new file mode 100644
index 0000000..b576ed9
--- /dev/null
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@@ -0,0 +1,12 @@
+This repository exists to help prove out site specific cbuildbot configurations.
+
+To check this out as a repo checkout:
+
+  repo init -u https://chromium.googlesource.com/chromiumos/chromite/abuildbot_config
+
+To perform a local build:
+
+  bin/cbuildbot --buildroot /tmp/test_buildroot \
+    --buildbot --debug --config_repo  \
+    https://chromium.googlesource.com/chromiumos/chromite/abuildbot_config \
+    sync-test-abuildbot