TBR: mojo.discovery: Prepare all repos for open-sourcing.

The CONTRIBUTING file is added to all repos, and also added
to the jiri-copyright tool so that repos can be automatically
checked and fixed.

I've run jiri copyright fix against all repos to fix up
outstanding issues.

MultiPart: 10/23

Change-Id: Icd196b18078f172d183ef0c0a555e19e972655b4
diff --git a/CONTRIBUTING b/CONTRIBUTING
new file mode 100644
index 0000000..799bc50
--- /dev/null
+++ b/CONTRIBUTING
@@ -0,0 +1,25 @@
+# Contributing to Vanadium
+
+Vanadium is an open source project.
+
+It is the work of many contributors. We appreciate your help!
+
+
+## Filing issues
+
+We use a single GitHub repository for
+[tracking all issues](https://github.com/vanadium/issues/issues)
+across all Vanadium repositories.
+
+
+## Contributing code
+
+Please read the
+[Contribution Guidelines](https://github.com/vanadium/docs/blob/master/community/contributing.md)
+before sending patches.
+
+**We do not accept GitHub pull requests**
+(we use [Gerrit](https://www.gerritcodereview.com/) instead for code review).
+
+Unless otherwise noted, the Vanadium source files are distributed under
+the BSD-style license found in the LICENSE file.