[bazel] Document need for --cc_output_directory_tag
[bazel] Document need for --cc_output_directory_tag

Change-Id: Ia47d3a3e9c23b63b1651dc1f638d917b3c302911
Bug: skia:12541
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/544636
Reviewed-by: Ben Wagner <53965154ffeecc4a10886eab9259e95965f2979a@google.com>
Commit-Queue: Ben Wagner <53965154ffeecc4a10886eab9259e95965f2979a@google.com>
Auto-Submit: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia