Add package comments

selector/doc.go

@@ -0,0 +1,8 @@
+/*
+Package selector is a way to load balance service nodes.
+
+It algorithmically filter and return nodes required by the client or any other system.
+Selector's implemented by Micro build on the registry but it's of optional use. One could
+provide a static Selector that has a fixed pool.
+*/
+package selector