[bazel] Docs ignore bazel's build directories
[bazel] Docs ignore bazel's build directories

Our site configs need another entry to ignore bazel build directories
when building documentation.

Signed-off-by: Drew Macrae <32d48ac45113625c0a04afe7343eae478a303684@google.com>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan