doc: Document required order of currentsong response

The parser implemented in libmpdclient requires the first key-value pair of the server response to be the file pair. This is due to the fact that libmpdclient scan pairs sequentially and first attempts to extract the file pair before parsing the currentsong response further. See: https://github.com/MusicPlayerDaemon/libmpdclient/blob/5c751a761ec9f71a43ee0e41cfff3208f31a58b8/src/song.c#L559-L563 Meta data encoded as pairs in the currentsong response will be ignored if they are placed before the file pair in the response.

doc: Document required order of currentsong response
3c955639 · Sören Tempel · bca96786 · 3c955639
Commit 3c955639 authored Apr 27, 2020 by Sören Tempel
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protocol.rst doc/protocol.rst +3 -1

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--- a/doc/protocol.rst
+++ b/doc/protocol.rst
@@ -389,7 +389,9 @@ Querying :program:`MPD`'s status

 :command:`currentsong`
    Displays the song info of the current song (same song that
-    is identified in status).
+    is identified in status). Information about the current song
+    is represented by key-value pairs, one on each line. The first
+    pair must be the `file` key-value pair.

 .. _command_idle: