Merge pull request #1902 from weaveworks/vendored-dep-management-doc

Document vendored dependency management commands

vendor/README.md

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+
+# Managing Vendored Dependencies with `git submodule`
+
+These operations result in staged but 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
+
+    ~/weave$ git submodule add https://example.com/organisation/module vendor/example.com/organisation/module
+
+## Update All Dependencies to Upstream `master`
+
+    ~/weave$ git submodule foreach git pull origin master
+
+## Force a Specific Dependency to a Particular Commit
+
+	~/weave$ (cd vendor/example.com/organisation/module && git checkout <commit-ish>)
+	~/weave$ git add vendor/example.com/organisation/module
+
+## Remove a Dependency
+
+	~/weave$ git submodule deinit vendor/example.com/organisation/module
+    ~/weave$ git rm vendor/example.com/organisation/module
+	~/weave$ rm -rf .git/modules/vendor/example.con/organisation/module
+