update robots.txt to disallow the community/ pages

Change-Id: I318308f7219b296d92039cba2b6f5ace321f697f
diff --git a/docs/html/robots.txt b/docs/html/robots.txt
index 503e4b1..f522220 100644
--- a/docs/html/robots.txt
+++ b/docs/html/robots.txt
@@ -14,4 +14,5 @@
 Disallow: /shareables/
 Disallow: /guide/tutorials/
 Disallow: /guide/samples/
+Disallow: /community/
 Sitemap: http://developer.android.com/sitemap.txt