Update documentation for `m` to clarify that it won't break Windows.
Update documentation for `m` to clarify that it won't break Windows.

R=maruel@chromium.org, vadimsh@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2076423005

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py