message: [doc] productivity: fix broken link
diff: @@ -76,7 +76,7 @@ Writing code
  ### Format C/C++/Protobuf diffs with `clang-format-diff.py`
  -See [contrib/devtools/README.md](contrib/devtools/README.md#clang-format-diff.py).
  +See [contrib/devtools/README.md](/contrib/devtools/README.md#clang-format-diff.py).
  ### Format Python diffs with `yapf-diff.py`
  