Add first version of sf-stream README

sf-stream/README.md

@@ -1 +1,39 @@
-# sf-stream
+# sf-stream
+sf-stream is the component that receives a live stream of frame data from 
+sf-buffers over ZMQ and assembles them into images. This images are then 
+sent again over ZMQ to external components. There is always only 1 sf-stream 
+per detector.
+
+It currently has 3 output streams:
+
+- **Full data full metadata** rate stream (send all images and metadata)
+- **Reduced data full metadata** rate stream (send less images, but 
+all metadata)
+- **Pulse_id** stream (send only the current pulse_id)
+
+In addition to receiving and assembling images, sf-stream also calculates 
+additional metadata and constructs the structures needed to send data in 
+Array 1.0 protocol.
+
+## Overview
+
+![image_stream_overview](../docs/sf_daq_buffer-overview-stream.jpg)
+
+sf-stream is a single threaded application (without counting the ZMQ IO threads)
+that is used for providing live assembled images to anyone willing to listen. 
+
+In addition, it also provides a pulse_id stream, which is the most immediate 
+pulse_id feedback we currently have in case we need to synchronize external 
+components to the current machine pulse_id.
+
+## ZMQ receiving
+
+## Image assembly
+
+## ZMQ sending
+
+### Full data full metadata stream
+
+### Reduced data full metadata stream
+
+### Pulse_id stream