Updated SVDRP help (markdown)

SVDRP-help.md

@@ -144,3 +144,30 @@ Set the audio volume to the given number (which is limited to the range 0...255)
 
 Exit vdr (SVDRP). You can also hit Ctrl-D to exit.
 
+## SVDRP reply codes
+
+    214 Help message
+    215 EPG or recording data record
+    216 Image grab data (base 64)
+    220 VDR service ready
+    221 VDR service closing transmission channel
+    250 Requested VDR action okay, completed
+    354 Start sending EPG data
+    451 Requested action aborted: local error in processing
+    500 Syntax error, command unrecognized
+    501 Syntax error in parameters or arguments
+    502 Command not implemented
+    504 Command parameter not implemented
+    550 Requested action not taken
+    554 Transaction failed
+    900 Default plugin reply code
+    901..999 Plugin specific reply codes
+
+
+
+Answers are in the format:
+
+    <reply code><-|space><text>\n
+
+In the last line returned as an answer to a command, the "-" will be replaced by a space character.
+