Build dev server as a java_binary

Update documentation and run_dev script to reflect reality.

Change-Id: If2468d9084d373b47c385eba3420d0ee55664750

gitiles-dev/BUCK

diff --git a/gitiles-dev/BUCK b/gitiles-dev/BUCK
index b50f58b..0ab7c53 100644
--- a/gitiles-dev/BUCK
+++ b/gitiles-dev/BUCK
@@ -1,5 +1,5 @@
 java_library(
-  name = 'dev',
+  name = 'lib',
   srcs = glob(['src/main/java/**/*.java']),
   deps = [
     '//gitiles-servlet:servlet',
@@ -15,3 +15,10 @@
   ],
   visibility = ['PUBLIC'],
 )
+
+java_binary(
+  name = 'dev',
+  deps = [':lib'],
+  main_class = 'com.google.gitiles.dev.Main',
+  visibility = ['PUBLIC'],
+)