Fix run instructions in README.md
Fix run instructions in README.md

TBR=janscheffler@chromium.org

Change-Id: I5c69ccb4fb4c311a7f025735b4691bcafdb75c58
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/1872029
Reviewed-by: Yang Guo <1cf0af8245a3a17a632a2c73531392b0f9761c76@chromium.org>
Commit-Queue: Yang Guo <1cf0af8245a3a17a632a2c73531392b0f9761c76@chromium.org>
Auto-Submit: Yang Guo <1cf0af8245a3a17a632a2c73531392b0f9761c76@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend