gn: Add a newline to fix a bulleted list in README.md.

Currently the bulleted list in the "What does 'done' mean?" section isn't
rendered (instead, it is shown as one paragraph with asterisks in the
middle). Adding a newline should fix this.

See https://chromium.googlesource.com/chromium/src/tools/gn/+/441de2f

Review URL: https://codereview.chromium.org/1153803002

Cr-Original-Commit-Position: refs/heads/master@{#331229}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 92acc5eca80b1cbd6fcf18a81795c5b74f9d3f06

tools/gn/README.md

diff --git a/tools/gn/README.md b/tools/gn/README.md
index 6173a51..f78765f 100644
--- a/tools/gn/README.md
+++ b/tools/gn/README.md
@@ -55,7 +55,8 @@
 Chromium and no one misses them.
 
 We will be "mostly" done when the following are true:
-  * All of the bots maintained by the Chrome infra team for Chromium and 
+
+  * All of the bots maintained by the Chrome infra team for Chromium and
     downstream of Chromium have been switched to GN. (Upstream projects
     like Skia and V8 can choose to stay on GYP if they like).
   * Any developer configurations we care about that don't have bots also