Adapt pipeline to transmit single line (2456x1) instead of 2456x4

- Modified recv_raw_rolling.py to handle 2456x1 BGR line format
- Fixed display dimensions (2456 tall x 800 wide)
- Updated 200fps-2456x4pix-cw.ini to start at Y=500
- Added detailed single line transmission docs to network_guide.md
- Updated README.md with quick start example using videocrop

ini/200fps-2456x4pix-cw.ini

@@ -15,9 +15,9 @@ Sensor digital gain=0
 
 [Image size]
 Start X=0
-Start Y=0
+Start Y=500
 Start X absolute=0
-Start Y absolute=0
+Start Y absolute=500
 Width=2456
 Height=4
 Binning=0