Update README

Author: coderdj

README

@@ -1,17 +1,68 @@
-DAX
-------
+# DAX
+D. Coderre, 2018. See license in LISCENSE file.
 
-Prerequisites
--------------
+## Prerequisites
 
 mongodb cxx driver
 CAENVMElib v2.5+
+Driver for your CAEN PCI card
+A DAQ hardware setup
+A MongoDB deployment
 
-Install
--------
+## Install
 
 make
-./main
 
+## Usage
 
+./main mongodb://localhost:27017/database
+
+The argument is the connection string to the dax database. 
+This database has to be configured as described in the 
+section 'database'. You may include a username and password 
+as well as any other syntax allowed by a MongoDB URI (it is
+parsed by the driver as a URI). 
+
+There is an optional third argument, which is an integer or 
+string. In case you run a single node per host the node will 
+identify itself by its hostname. But if you run two nodes on 
+one host the hostname is no longer unique. The argument is appended
+to the hostname (connected with an underscore '_') in order to
+allow definition of unique hosts.
+
+For example, if you run on host **daq00**
+
+**One node:**
+
+./main {MONGO_URI}
+
+Here we put no argument. This instance will be addressed by
+hostname "daq00".
+
+**Two nodes one host:**
+
+./main {MONGO_URI} 0
+./main {MONGO_URI} 1
+
+Here we start two instances with two arguments. One instance
+will be addressed as "daq00_0" and the other as "daq00_1".
+
+Easy peasy.
+
+## Database Setup
+
+You need to provide connectivity to a mongodb database using the URI.
+This database should have the following collections.
+
+**control:** is where commands go. The storage requirements are basically
+zero since commands are deleted after all addressees have acknowledged
+them.
+
+**status:** should be configured as a capped collection. Each readout
+node will write it's status here every second or so.
+
+**options:** is where settings docs go. When sending the 'arm' command
+the name of the options file should be embedded in the command doc.
+If the reader can't find an options doc with that name it won't be
+able to arm the DAQ.