Add README file about current state

README

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+Osmocom Iuh expermientation code
+(C) 2015 by Harald Welte <laforge@gnumonks.org>
+
+This code is a playground for implementing something along the lines of
+the an Iuh interface of a HNB-GW.  The intent is to later integrate this
+with OsmoNITB + OsmoSGSN, in order to have 3G capable 'network in the
+box'.
+
+h1. Building
+
+Just go to the 'src/' directory and type make.  As external library
+dependencies, you will need
+* libosmocore from git://git.osmocom.org/libosmocore
+* libasn1c from git://git.osmocom.org/libasn1c
+
+h1. Using
+
+there's not much to use yet.  But if you run the 'hnbgw' executable,
+it will open a listening SCTP socket and wait for incoming Iuh
+connections.  It will accept any HNB-REGITER-REQUEST, so the homeNodeB
+should start to establish RUA and RANAP (which we haven't implemented
+yet).
+
+h1. Regenerating C code from ASN.1 source
+
+In order to re-generate the C source code from the ASN.1 source,
+you will need a modified asn1c which has the following features:
+* APER support (the patch from Eurecom, or its forward-ported version
+  from the aper branch of git://git.osmocom.org/asn1c)
+* support for prefixing the generated types (aper-prefix branch of
+  git://git.osmocom.org/asn1c)