message: Document march flag
  Summary: Ref T16509
  Reviewers: jamiep, davidn, #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved, vladimirm
  Maniphest Tasks: T16509
diff: @@ -50,8 +50,9 @@ You can now build TensorFlow by following the instructions here:
  The default compilation option `-march=native` optimizes the generated code for
  your machine's CPU type. However, if building TensorFlow for a different CPU
  type, you can use a more specific optimization option. For example, the
  -Graphcore TensorFlow distributed in the Poplar SDK is built with
  -`-march=skylake-avx512`.
  +Graphcore TensorFlow packages distributed in the Poplar SDK are built with:
  +* `-march=skylake-avx512` for the Intel package,
  +* `-march=znver1` for the AMD package.
  See the GCC manual for more information.
  ### Building against custom PopLibs
  