lint: add missing package level comments (#3302)

profiling/cmd/main.go

@@ -16,6 +16,8 @@
  *
  */
 
+// Binary cmd is a command-line tool for profiling management. It retrieves and
+// processes data from the profiling service.
 package main
 
 import (

xds/internal/balancer/balancer.go

@@ -16,6 +16,7 @@
  *
  */
 
+// Package balancer installs all the xds balancers.
 package balancer
 
 import (