doc: document applehttp protocol

The documentation might be extended once/if a live/store override option
will have to be provided for non-compliant segmenter.

doc/protocols.texi

@@ -19,6 +19,22 @@ supported protocols.
 
 A description of the currently available protocols follows.
 
+@section applehttp
+
+Read Apple HTTP Live Streaming compliant segmented stream as
+a uniform one. The M3U8 playlists describing the segments can be
+remote HTTP resources or local files, accessed using the standard
+file protocol.
+HTTP is default, specific protocol can be declared using the "+"
+specifier.
+
+@example
+applehttp://host/path/to/remote/resource.m3u8
+applehttp+http://host/path/to/remote/resource.m3u8
+applehttp+file://path/to/local/resource.m3u8
+@end example
+
+
 @section concat
 
 Physical concatenation protocol.