Add command to extract build info from metadata

This will allow to recreate the metadata after patching the FS.

PUBLISHED_FROM=dae228bbf49d71f383e4dc52316cf98aba3914f5

docs/design-concept/intro.md

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+---
+title: Design Concept
+---
+
+Mongoose is a multi-protocol networking library that implements non-blocking,
+asyncronous IO and provides event-based API. It has three basic data structures:
+
+- [`struct mg_mgr`](#TODO) is an event manager that holds all active
+  connections
+- [`struct mg_connection`](#TODO) describes a connection
+- [`struct mbuf`](#TODO) describes data buffer (received or sent data)
+
+Connections could be either *listening*, *outbound* or *inbound*.  Outbound
+connections are created by [`mg_connect()`](#TODO) call.  Listening connections
+are created by [`mg_bind()`](#TODO) call.  Inbound connections are those
+accepted by a listening connection.  Each connection is described by [`struct
+mg_connection`](#TODO) structure, which has a number of fields like socket,
+event handler function, send/receive buffer, flags, et cetera.
+
+Mongoose usage pattern is to declare and initialize event manager, create
+connections and create an event loop by calling [`mg_mgr_poll()`](#TODO) in a
+loop.  [`mg_mgr_poll()`](#TODO) iterates over all sockets, accepts new
+connections, sends and receives data, closes connections, and calls event
+handler functions for the respective events.