small tweaks to readme and .gitignore (dart-lang/browser_launcher#2)

diff --git a/pkgs/browser_launcher/.gitignore b/pkgs/browser_launcher/.gitignore
index 49ce72d..ec8eae3 100644
--- a/pkgs/browser_launcher/.gitignore
+++ b/pkgs/browser_launcher/.gitignore
@@ -1,3 +1,4 @@
+# Don’t commit the following directories created by pub.
 .dart_tool/
 .packages
 pubspec.lock
diff --git a/pkgs/browser_launcher/README.md b/pkgs/browser_launcher/README.md
index afda081..6b10c54 100644
--- a/pkgs/browser_launcher/README.md
+++ b/pkgs/browser_launcher/README.md
@@ -1,3 +1,5 @@
-## What is this?
-This package provides a standardized way to launch web browsers. Currently, Chrome is the only supported browser. Support
-for other browsers will be added in the future.
+Provides a standardized way to launch web browsers.
+
+Currently, Chrome is the only supported browser.
+
+Support for other browsers will be added in the future.