multi: add README's for all sub-packages

lnwallet/README.md

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+lnwallet
+=========
+
+[![Build Status](http://img.shields.io/travis/lightningnetwork/lnd.svg)]
+(https://travis-ci.org/lightningnetwork/lnd) 
+[![MIT licensed](https://img.shields.io/badge/license-MIT-blue.svg)]
+[![GoDoc](https://img.shields.io/badge/godoc-reference-blue.svg)]
+(http://godoc.org/github.com/lightningnetwork/lnd/lnwallet)
+
+The lnwallet package implements an abstracted wallet controller that is able to
+drive channel funding workflows, a number of script utilities, witness
+generation functions for the various Lightning scripts, revocation key
+derivation, and the commitment update state machine. 
+
+The package is used within `lnd` as the core wallet of the daemon. The wallet
+itself is composed of several distinct interface that decouple the
+implementation of things like signing and blockchain access. This separation
+allows new `WalletController` implementations to be be easily dropped into
+`lnd` without disrupting the code base. A series of integration tests at the
+interface level are also in place to ensure conformance of the implementation
+with the interface.
+
+
+## Installation and Updating
+
+```bash
+$ go get -u github.com/lightningnetwork/lnd/lnwallet
+```