[turbolizer] Fix formatting in readme file

The current formatting makes the build command seem to be one line,
whereas it should be two.

Change-Id: I9abe7cf3351aae1f1df51bf1e3ca46a0ed2c012b
Reviewed-on: https://chromium-review.googlesource.com/1225708Reviewed-by: Daniel Clifford <danno@chromium.org>
Commit-Queue: Stephan Herhut <herhut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55904}