Add vendoring docs

vendor/README.md

@@ -0,0 +1,17 @@
+# Managing Vendored Dependencies with `gvt`
+
+These operations result in uncommitted changes to your
+branch; you will need to commit them as normal. Execute them in the
+root of your checkout.
+
+## Adding a New Dependency
+
+    ~/scope$ gvt fetch example.com/organisation/module vendor/example.com/organisation/module
+
+## Updateing a Specific Dependancy
+
+    ~/scope$ gvt update example.com/organisation/module vendor/example.com/organisation/module
+
+## Remove a Dependency
+
+    ~/scope$ gvt delete example.com/organisation/module vendor/example.com/organisation/module