Document that the war built by 'bazel build gerrit' contains PolyGerrit
Document that the war built by 'bazel build gerrit' contains PolyGerrit

Since change I9b92194c61 'bazel build gerrit' no longer builds the GWT
UI.

Change-Id: I7e01b22dccdb9dd9bd6bdb4b5eb3098098c3c84e
Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>

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