Doc: add package docs (#296)

* Doc: add package docs

Add short package level docs to make godoc looks nicer.
Add some badges to the README.

* correct url

middleware/pkg/dnsrecorder/recorder.go

@@ -1,3 +1,4 @@
+// Package dnsrecorder allows you to record a DNS response when it is send to the client.
 package dnsrecorder
 
 import (

middleware/pkg/dnsutil/doc.go

@@ -0,0 +1,2 @@
+// Package dnsutil contains DNS related helper functions.
+package dnsutil

middleware/pkg/edns/edns.go

@@ -1,3 +1,4 @@
+// Package edns provides function usefull for adding/inspecting OPT records to/in messages.
 package edns
 
 import (

middleware/pkg/storage/fs.go

@@ -1,3 +1,4 @@
+// Package storage abstracts away where middleware can store assests (zones, keys, etc).
 package storage
 
 import (