Expanded the README with some extra details

README

@@ -7,6 +7,29 @@ A robust packetised version of the JPEG image format.
 
 Uses the Reed-Solomon codec written by Phil Karn, KA9Q.
 
+ENCODING
+
+$ ssdv -e -c CALLSIGN -i ID input.jpeg output.bin
+
+This encodes the 'input.jpeg' image file into SSDV packets stored in the 'output.bin' file. CALLSIGN (an alphanumeric string up to 6 characters) and ID (a number from 0-255) are encoded into the header of each packet. The ID should be changed for each new image transmitted to allow the decoder to identify when a new image begins.
+
+The output file contains a series of SSDV packets, each packet always being 256 bytes in length. Additional data may be transmitted between each packet, the decoder will ignore this.
+
+DECODING
+
+$ ssdv -d input.bin output.jpeg
+
+This decodes a file 'input.bin' containing a series of SSDV packets into the JPEG file 'output.jpeg'.
+
+LIMITATIONS
+
+Only JPEG files are supported, with the following limitations:
+
+ - YUV/YCbCr colour format
+ - Width and height must be a multiple of 16 (up to a resolution of 4080 x 4080)
+ - Baseline DCT only
+ - The total number of MCU blocks must not exceed 65535
+
 INSTALLING
 
 make