encoding/binary: use list format in docstrings

encoding/binary: use list format in docstrings

This looks way better than the code formatting.

Similar to CL 597656.

Change-Id: If404c952ece384aea096f2394bd475a601627a79
Reviewed-on: https://go-review.googlesource.com/c/go/+/597657
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>