Refactor Mongoose documentation

PUBLISHED_FROM=e9a4e5c7b4a1d03b93a2a79e29de19e60e919929

docs/dns/client_example.md

@@ -0,0 +1,5 @@
+---
+title: DNS client example
+---
+
+TBD

docs/dns/intro.md

@@ -0,0 +1,8 @@
+---
+title: DNS
+items:
+  - { name: server_example.md }
+  - { name: client_example.md }
+  - { name: ../c-api/dns.h/ }
+  - { name: ../c-api/dns_server.h/ }
+---

docs/dns/server_example.md

@@ -0,0 +1,5 @@
+---
+title: DNS server example
+---
+
+TBD