Add overview section to README

README.markdown

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+## Overview **HMS Hub** manages the delivery and tracking of phone-based
+notifications to end recipients.  It is particularly well suited for
+environments where recipient phones are frequently inaccessible; this may be
+due to limited signal range or access to power, common in some developing
+countries.
+
+The hub supports SMS and IVR (voice message) delivery methods and comes
+bundled with support for [Nexmo](https://www.nexmo.com) (SMS) and
+[IntellIVR](http://www.yo.co.ug/index.php?option=com_content&task=blogcategory&id=25&Itemid=85)
+(IVR).  You can also develop and plug in additional delivery providers (see
+`app/models/delivery/provider` for example implementations).
+
+This software was developed to support objectives outlined in the CCPF
+program.
+
+### About the CCPF Program The VillageReach CCPF program, CHIPATALA CHA PA
+FONI, means "Health Center by Phone" in the Malawian language of Chichewa.
+The program is focused on maternal & child health improvement, through
+increased access to basic health information, and prompting towards earlier
+interaction with the health system.  The program has two components:  a
+toll-free hotline for pregnancy & infant health advice and referrals,  and a
+health-tip messaging system, which pushes SMS and voice messages out to
+rural clients who have been enrolled in the tips system.  The program
+enjoyed a successful pilot over 2 years, from 2011-2013, handling hundreds
+of callers per week,  and is now in the process of expanding its reach.
+
+The software used by the hotline workers to record caller interaction is
+[mnch-hotline](https://github.com/BaobabHealthTrust/mnch-hotline), developed
+by the Malawian health-software company
+[Baobab Health Trust](http://baobabhealth.org/). The software to handle the
+tips-message distribution, [HMS-Hub](https://github.com/dhedlund/hms-hub),
+and [HMS-Notifier](https://github.com/dhedlund/hms-notifier), were developed
+by VillageReach.  All components are in active production use in Malawi.
+
+### Messaging System The tips-messaging system is designed to operate
+robustly in a environment with intermittent connectivity, and multiple
+remote messaging sources.  The Hub software is intended to be on a
+relatively better-connected server.  It centralizes handling of all the
+message-delivery gateways (SMS, IVR, email, etc) and serves as a capable
+store-and-forward.  Each authorized instance of the Notifier software
+connects to the Hub periodically to issue a new set of message requests, and
+receive data on message-attempt results.  Both apps expect an unreliable
+Hub-Notifier connection, and to a lesser extent, an unreliable connection
+between the Hub and its messaging gateways.  The Hub also handles its own
+retries of failed messages, for when the gateway does not.
+
+In production practice, in Malawi, the Hub is in a telco server room, on the
+telco's network connection.  The currently single Notifier instance on the
+hotline server, located in a rural district hospital, where the hotline
+workers have local oversight in the pilot program.  The Notifier connects
+via a USB dongle, over a private APN on the telco's 2G network.  The
+software handles regular downtime between those servers, and the Hub handles
+SMS and voice messages that often take multiple retries to reach customer
+phones, which are often out of range or powered down.
+
+
 ## Getting Started
 It is assumed that you have ruby version 1.9.3, are using bundler and have the necessary mysql headers to compile the `mysql2` gem.