Fix formatting of table.

The gitiles rendering is [broken](https://screenshot.googleplex.com/6AvjT3ysbtyAETw), as it requires empty cells to be [whitespace between column dividers](https://gerrit.googlesource.com/gitiles/+/HEAD/Documentation/markdown.md#tables)

Test: just updating doc

Bug: 264528457

Change-Id: I0fa8a241c25e4031b80c635db460af0d2e567456