[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}

tools/turbolizer/README.md

@@ -10,8 +10,8 @@ the '--trace-turbo' command-line flag.
 
 Turbolizer is build using npm:
 
-  npm i
-  npm run-script build
+    npm i
+    npm run-script build
 
 Afterwards, turbolizer can be hosted locally by starting a web server that serve
 the contents of the turbolizer directory, e.g.: