Add description of bootstrap-repo.sh

Change-Id: I764d63d23accf564b183e6a7032b2db8683cf495
diff --git a/developer/README.md b/developer/README.md
index e2c0350..782a151 100644
--- a/developer/README.md
+++ b/developer/README.md
@@ -14,3 +14,15 @@
 ```
 python imagebuilder.py -f ../../helm-charts/examples/filter-images.yaml -x
 ```
+
+## Download the full CORD source tree and optionally apply Gerrit patchsets
+
+The `bootstrap-repo.sh` script installs the `repo` tool, uses it to
+download the CORD source tree, and optionally applies one or more
+patchsets from Gerrit to the tree.  It may be useful when
+bootstrapping a new environment for development or testing.
+
+Usage:
+```
+bootstrap-repo.sh [-p <project:change/revision>]
+```