update README

README.md

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 # joinmarket-clientserver
 Joinmarket refactored to separate client and backend operations
 
+Motivation: By separating the code which manages conversation with other
+Joinmarket participants from the code which manages this participant's Bitcoin
+wallet actions, we get a considerable gain at a minor cost of an additional layer:
+code dependencies for each part are much reduced, security requirements of the 
+server/daemon layer are massively reduced (which can have several advantages such as
+it being more acceptable to distribute this layer as a binary), and client code
+can be written, implementing application-level logic (do join with coins X under condition X)
+using other Bitcoin libraries, or wallets, without knowing anything about
+Joinmarket's inter-participant protocol. An example is my work on the Joinmarket
+electrum [plugin](https://github.com/AdamISZ/electrum-joinmarket-plugin).
+
+It also
+means that updates to the Bitcoin element of Joinmarket, such as P2SH and segwit, should
+have extremely minimal to no impact on the backend code, since the latter just implements
+communication of a set of formatted messages, and allows the client to decide on
+their validity beyond simply syntax.
+
+Joinmarket's own [messaging protocol] is thus enforced *only* in the server/daemon.
+
+The client and server currently communicate using twisted.protocol.amp, see
+[AMP](https://amp-protocol.net/) which is a very clean asynchronous messaging protocol,
+and the specification of the communication between the client and server is isolated to
+[this](https://github.com/AdamISZ/joinmarket-clientserver/blob/master/jmbase/commands.py) module.
+
+The server is currently implemented as a daemon (see `scripts/joinmarketd.py`), in future
+it may be convenient to create the option to run it within the same process as the client.
+
 Use `virtualenv` to manage dependencies, e.g. follow this workflow:
 
     git clone https://github.com/AdamISZ/joinmarket-clientserver