doc/ffserver: rework introducing paragraphs of the "description" chapter

In particular, add some markup, fix empty line, and merge it with "How
does it work?" section.

doc/ffserver.texi

@@ -16,34 +16,33 @@ ffserver [@var{options}]
 @chapter Description
 @c man begin DESCRIPTION
 
-ffserver is a streaming server for both audio and video. It supports
-
-several live feeds, streaming from files and time shifting on live feeds
-(you can seek to positions in the past on each live feed, provided you
-specify a big enough feed storage in ffserver.conf).
+@command{ffserver} is a streaming server for both audio and video. It
+supports several live feeds, streaming from files and time shifting on
+live feeds (you can seek to positions in the past on each live feed,
+provided you specify a big enough feed storage in
+@file{ffserver.conf}).
 
 This documentation covers only the streaming aspects of ffserver /
 ffmpeg. All questions about parameters for ffmpeg, codec questions,
 etc. are not covered here. Read @file{ffmpeg.html} for more
 information.
 
-@section How does it work?
-
-ffserver receives prerecorded files or FFM streams from some ffmpeg
-instance as input, then streams them over RTP/RTSP/HTTP.
+@command{ffserver} receives prerecorded files or FFM streams from some
+@command{ffmpeg} instance as input, then streams them over
+RTP/RTSP/HTTP.
 
-An ffserver instance will listen on some port as specified in the
-configuration file. You can launch one or more instances of ffmpeg and
-send one or more FFM streams to the port where ffserver is expecting
-to receive them. Alternately, you can make ffserver launch such ffmpeg
-instances at startup.
+An @command{ffserver} instance will listen on some port as specified
+in the configuration file. You can launch one or more instances of
+@command{ffmpeg} and send one or more FFM streams to the port where
+ffserver is expecting to receive them. Alternately, you can make
+@command{ffserver} launch such @command{ffmpeg} instances at startup.
 
-Input streams are called feeds, and each one is specified by a <Feed>
-section in the configuration file.
+Input streams are called feeds, and each one is specified by a
+@code{<Feed>} section in the configuration file.
 
 For each feed you can have different output streams in various
-formats, each one specified by a <Stream> section in the configuration
-file.
+formats, each one specified by a @code{<Stream>} section in the
+configuration file.
 
 @section Status stream