Introduced service `popular`

[demos/kafka/wordcount] / popular

diff --git a/popular b/popular
new file mode 160000 (submodule)
index 0000000..e88db15
--- /dev/null
+++ b/popular
@@ -0,0 +1 @@
+Subproject commit e88db15eafe64ac083d066be29ad94058930bb5d